This is what I'd like to do; build a new PC with 2 internal hard drives, both bootable, with different OS's.  
I know I can have a single drive, that is multi-bootable to different OS's, but I have a requirement where I need 2 different OS's, on  different drives.
 
What do I need to buy for hardware?
 
I put "noob" in the subject because I don't know the answer to that question, and I'm trying to save some time, in trying to figure out what I need to buy.  I have heard of hot-swapable drives.... SATA.  But what I'm looking for here is, what's the name of the device that I need to look for, to give me 2 internal hot-swapable drives, each bootable?
 
Thanks!

You just need to buy two different SATA hard drives.  Connect both to your motherboard.  Install your operating systems on each drive.  That's all there is to it.  You don't need any extra hardware besides a DVD drive to install Vista or XP.

 
I did some more looking around, and found what I was referring to:
http://www.tigerdirect.com/applica [...] VIEWS#tabs
 
So it looks like I'd buy one of these, along with 2 SATA drives.  And get the spare tray that's on the right side of the page, to put the 2nd drive in.  Anyone ever try one of these?

Why are you going to be swapping them out? What OSs are you dual booting to?

 
XP and Server 2003.
 
I can't use a dual boot setup, software will be on the XP machine that won't work in a dual boot setup.

I don't know what software you mean, but you can change the boot order in BIOS very easily. Some even have a boot screen outside of the BIOS, I think my DQ6 does, let me check.

Yup, F12 loads a boot menu, choose HD and you get a sub menu that allows you to choose the drive.

Dual boot on one harddrive is harder.
 
But with two hard drives, just press F8 during the first 5 seconds the computer is turned on.
 
And make changes in bios so that the OS you use most that HD is in 1st place, when you are not pressing F8.

 
I ended up buying one of those swappable drive trays (http://www.tigerdirect.com/applications/searchtools/item-details.asp?EdpNo=1196207&body=MAIN)
 
And I bought an extra tray and drive.  I just pop out one drive and pop in the other.  And fact I just ordered a 3rd set.  The first one is for my wife's work-at-home job that doesn't allow dual-boot drives, the 2nd is for an evaluation copy of Windows Server 2003 that I'm using to study for an MCP test, and the 3rd will be for the kids games.
 
It costs more than dual boot but, it works great and is very convenient!

Concur with Zorg.
 
   Dual Boot with 2 HDD is easy.  I have two Pairs of Raid 0 HDD.  I installed XP Pro On one pair,  Disconnected, and Installed Visa Bus on 2nd Pair.  Reattached first pair and Have dual boot selectable on start up using F12 (Have DQ6 board).  I prefer this route to a software boot menu.  I also Have a removable IDE HDD (NOT hot swapable) that I could install a 3rd Operating system on.
 
Go for it.