2 Hard drives or 1

If What are you going to do with Ubuntu? If you wanted to, you can get the free VMware player and download any version of Ubuntu as a VM.

I tried Linux years ago with Fedora Core 1 & 2 but I thought that it was not ready for prime time.
I want to try Linux again due to security issues with Windows. I am tired of hearing every week that my Windows box is open to attack again.
I want to see how much of my computing life can be done with Linux, getting away from Windows. I have a least 3 Windows programs that I must have along with some games.
So the idea is to have Linux I can boot into with full hardware support.

Then try out the VMware solution, it will prep you till your ready.

One hard drive will suffice: Partition it with fdisk from your Windows installation disk or, preferably, from a Knoppix disk, so that you will have two partitions of about 20G each, one for each of the operating systems, and the remainder of your hard disk blank and thus available for any future use you might want to make of it. Install Windows first, do so on the first partition, and make that partition "bootable", thus writing an MBR and a Partition Table to its first block of 512 bytes. Then install Ubuntu on the second partition. That Ubuntu installation should include a Grub package which, during the course of its installation, should allow you the opportunity of making it, Grub, aware of your existing Windows partition; do so. With all the installations completed you will then have a dual-boot box along with Grub to allow you the choice of either any time you boot it up. In addition, you will have plenty of disk space available for any subsequent installations you might choose to make.
Let me add here that I forgot to mention the need for a swap partition (that's a memory thing, and you know how old saws are with memory): Give your hard drive three partitions - two of 20G or so each for the operating systems and a third of one or two Gigs to serve as a swap partition for your Ubuntu system.

I would recommend the VM ware option. Since you aren't highly experienced with Linux, it will allow you to (depending on which system you install it i.e. linux as the main system with an XP VM ware image or visa versa) easily switch between operating systems w/out having to reboot all the time. I would recommend Windows with a linux VM ware image. That way, when you are playing games, you can shut down the image so it doesn't consume resources.

Edit: One hard drive will allow you to do this just fine. You don't even need a separate partition. VMWare will just make a virtual "disk" on your current partition, which is basically just a large file that the system operates within. You can "partition" the file as you see fit from within the virtual operating system.

Thanks for the info, it is really a big help. One question though, does VMWare fully support new hardware?
The system I am building is a new Core Duo machine.

Core Duo E6600
Asus P5B Deluxe (P965)
Nvidia 7900 GT (Asus)
SATA HD (Seagate)
Plextor 760A DVD (IDE)
Creative X-Fi
2 GB Ram (Corsair)

I don't want to start a flame war here, but installing a Unix system within a Microsoft system just doesn't make much sense in your case. VMware might fill some important niches in a corporate environment where an IT Department is available for managing the extra ragmarole, but if you want a simple and direct solution then you should opt for the simple and direct path. True, some Linux distributions do present difficulties to the neophyte, but Ubuntu, SUSE, and Fedora (to name a few) are not among them: These are straightforward, logical distributions which will do for you what you expect of them. As for security, remember that any system which you run within a Windows system will itself be subject to attacks which penetrate that Windows system.

That is a very good point about VMWare, thanks. I will have to do some more research before I decide. On some other forumz a number of people have gone with the multiple hard drive soloution that does not touch their windows drive but allows them to try Linux. I do not have a problem with spending an extra $100 for a second hard drive.

I guess it all depends on what you want. I personally run RHWS 4 at work with a Windows VMWare image, but at home I have 2 separate computers.

In my opinion, you can't beat the convenience that VMWare offers in a situation where you need to run both OS types, but don't have two computers. If I had to restart every time I wanted to change what OS I was in, I'd shoot myself.

Oldsaw is right, it would probably be easy enough for you to get a straight forward Ubuntu or Linux system up and running pretty easily, but do you want to have to reboot into windows when you decided to play a game or use a utility?

Like I said, it depends on what you want. And if you do decide to use VMWare, you still have tto choose to run Windows or Linux natively  

I live and work completely in Linux except for gaming. One can do just about everything one needs to do in linux that I'd say more than 99.9% of people need to do. Except for gaming.

There are enough users that nearly all common hardware is supported and nearly all common software application types are covered. More and more people are developing for both platforms or are moving their apps to the web to make it OS independent.

The toughest hurdle left for me is to overcome the years of Windows centric optimization for 3D graphics so developers will have a reason to want to develop for Linux. We're still a ways off for that. Starting with stable, vendor supported drivers with good 3d accelleration.

I have run mixed Linux/Windows systems. Getting back to the original question of 1 vs. 2 disks, I would suggest 2. You can wedge two or more OSes onto a system, and use System Commander, Grub, or whatever to boot them, but using two disks makes it much less likely that some partition table or hard disk problem will blow both OSes out of the water. You may particularly be able to use Linux to fix XP, even NTFS XP. On one disk, you are susceptible to partition problems, particularly on re-installs, causing multpile difficulties. Just better to go to two if you can afford them. Plus smaller disks are frequently in a nice price point in the market.