How do I partition the hard drive, for example, partition 20-30 gb specifically for windows?

Are you doing a fresh install and want to just partition your hard disk?
 
Is the disk RAW?
 
Do you just want to create an extra partition on the drive thats currently running windows, but not to reinstall the OS?

It's best to do it during a clean install, on a new HD. If you allready have the drive in use, I like Partition Magic v8, Drive Image is another one. Even Digital Dolly a free unix/linux utility can do it to. There is a free live CD version of DD that is more user friendly.

If you already have the OS installed, the easiest way that I'm familiar with is to use Partition Magic.

if you are doing a clean install on a new drive.
 
Simply follow the install procedure, but when it comes to creating the partition. Make the partition around 30000MB (assuming you want a 30GBish Windows partition)
 
Then after the OS has installed. Click Start then right click My Computer and click Manage.
Then click disk management. There will be a graphical representation of your disk showing XX GB of unallocated space. Right click that area and click create partition following the simple onscreen instrustions that the wizard gives you.

Also you will have to give the partition size on MB
Converting GB to MB is easy
 
it goes like this
GB*1024=MB
SOoo like for a 30GB partition
30*1024=30720MB
 
 
just so you dont end up with like 29.297GB or something weird...which you would if you entered 30000MB

Get Acronis Disk Director. You can alter partitions without having to re-install.

partition magic does that too.
 
but partition magic makes it easy as a snap, very easy to use GUI

I am getting a new hard drive in a few days and I thought to make it faster that I would try  to partition it specifically for windows, leaving the rest for games, music photographs, and whatever. As you might have ascertained from the question, I am a novice at this computer stuff and jargon. thank you for answering my question.

Thank you for your response. I am getting a new system in a few days and I thought I would try something I read, partition the hard drive for windows, which would give me faster access time. I am a novice at this and trying to learn the most advantageous use of the computer.

If you're setting up a new disk versus trying to rearrange the partitions on an existing disk, then consider using the setup software that comes with a new retail boxed disk. All the major hard disk manufacturers provide some sort of GUI based software to allow you to partition and format a new disk either by booting from a CD or floppy or by running the setup software in Windows.
 
If you're getting the OEM version of a drive you can just download the setup software from the website of the drive's manufacturer.
 
-john

Thank you for your input.  The hard drive is a Dell 160 gb stata 7200rpm. You 're saying that I should receive a CD with the shipment that will have softwae (i.e.) instructions for this partition procedure? Or, I should be able to go to Dell's website and download software that will allow me to partition the drive?

Hate to be a canonical geek, but ... that's what I am, actually. Strictly speaking, there are no "Dell" hard drives. You may have bought the hard drive from Dell but I'm 99.99999% sure it was made by one of Western Digital, Seagate, Hitachi, et cetera.  
 

The manufacturer's CD would be included if you purchased the so-called retail box. This is just the hard drive as sold in the box that you would see in Best Buy, Circuit City, Wal-Mart and such. Many online sellers will also sell a hard drive as an OEM for ostensibly a little less money. The term OEM derives from the phrase "Original Equipment Manufacturer". An OEM drive is just the drive without any extra frills. No pretty packaging. No instruction/install manuals/pamphlets/CD. Usually no SATA cable either, though I'm not sure what Dell might do in this situation.
 
Do you know which you got? If it turns out they send you an OEM drive with no install CD, you can download the install software, maybe even an image for an install CD, from the drive manufactuer's website. If you need to go this route and have trouble locating what to download, just post the make and model of the drive here and someone should help point you in the right direction.
 
Out of curiosity, what system will you be installing the new drive into? (Is it a Dell also?)
 
-john, the redundant legacy dinosaur

OK, I'm a bit confused.  First you say that you are "getting a new system in a few days", then you say that you are "getting a new hard drive in a few days."  I hate to be a stickler, but which is it - a new whole computer system, or just a new hard drive?  
 
Also, If it's a new system, will it have XP already loaded on the hard drive?  If so, then you just need to purchase a 3rd party program as has been mentioned already like partition magic, acronis, etc...
 
 
Now if you just are getting a new hard drive...  as has already been mentioned, ... since you are wanting to re-install XP all you have to do is set your computer to boot from the CD.  Then put your XP install CD in the CD drive and reboot, or turn on the computer.  You may have to hit F8, or hit space bar, etc..  but once it start to load XP, in a few min  it will ask you what drive to install on.  When you tell it that drive,  It will then show you the current partition if there is one and then ask you about deleting the partition, etc...  I always have it first delete the whole partition, then re-create the partition(s).  It is at this time that you can choose to create multiple partitions.  You just have to tell it what size to make each partition.  After that it will tell you that you need to "format" the partitions.  Say "yes" and it will do it for you.  You can chose between "quick" or "normal" formating speeds.  I'm not sure how much better "normal" is, but "quick" sure is nice.  I usually pick "quick" unless setting up a RAID, or if I have had any drive problems.

OK, it looks like maybe I misunderstood. I was actually responding to the post where the OP said

and didn't see the post right after this where the OP said

So now I'm not sure exactly what the configuration of the system is and what the OP wants to do with it.  :?  
 
My best guess at this point is that the OP is expecting the arrival of a new Dell system with a single 160GB hard drive in it. When it arrives he expects it will have a single partition using the entire capacity of the drive. What he wants to try is to create two partitions on the 160GB drive. One will be about 20-30 gb  and contain the Windows operating system as it was when the Dell was shipped. The other will be the remainder of the disk and will be used for documents and other data.
 
That's my guess. Am I close? If so, that might (or might not) complicate things a bit. Please clarify what you have and what you want to keep before you start deleting data.  :!:  
 
-john

 
Add to the list Gparted - There is now a stand alone live CD with the full GUI version. Very similar to partition magic on terms of resizing and creating/deleting partitons. No command lines or Linux geek points required to use.

 
Unless you have a specific need, like installing two operating systems, then don't bother. Make it all one big partition.

Pardon the lack of specificity regarding future acquisition of hard drive or a new system. I am receiving a a DELL Dimension E521 small mini tower AMD Athalon 64 x2 dual core 3800(2.0 Ghz) Windows XP Media Center No RAID inclusive of 160 Gb SATA Hard drive @ 7200 rpm.

 
One partition.

That's what I would like to do; however; it's just a theoretical concept at this moment as I read that doing this may increase access time as an instruction will not have to traverse the entire system , only the windows partition, am I correct? It will be a new system and not just a new hard drive. The system will be a DELL E521, small mini tower, AMD Athalon 64x2 Dual core 3800 (2.0Ghz) Windows XP Media Center, No RAID, inclusive of SATA Hard Drive @7200 rpm.

 
With one 160GB drive it won't make any difference.