Confusion Over XP Products

Hey guys. I am hoping to purchase a notebook computer, but it has Windows Vista on it. I want to backport it to Windows XP, because most of the software I need are compatible with it. I am confused over these two products...

http://www.circuitcity.com/ssm/Micr...id/113706/rpem/ccd/productDetail.do#prodspecs

http://www.bestbuy.com/site/olspage...=product&tab=2&id=1083713449105#productdetail

One of them is $99.99. I was wondering if I just need to purchase that to change my computer to Windows XP. Also, is it a 32-bit or a 64-bit OS?

I also have some confusion over this Wikipedia article:

Advantages
The primary benefit of moving to 64-bit is the increase in the maximum allocable system memory (RAM). A single process on a 32-bit Windows operating system is limited to a total of 4 GB, which is typically equally divided between Kernel and application usage. Windows XP x64 can support much more memory; although the theoretical memory limit a 64-bit computer can address is about 16 exabytes, Windows XP x64 is limited to 128 GB of physical memory and 16 terabytes of virtual memory. These limitations are mostly theoretical as no workstation-class hardware is able to support this much memory or disk space.

from Wikipedia, Windows XP Editions

 

You need to buy the full version for $199. The upgrade version ($99) only works if you have Win98, ME or 2000.

They are both 32-bit, the only 64-bit version of XP is XP Professional 64-bit Edition.

 

Might I suggest you buy this instead?
http://www.newegg.com/Product/Product.aspx?Item=N82E16832116400

It's XP Professional (I find it hard to go back to home, but then again I actually use lots of the pro features). This is also 32 bit, but you don't want 64 bit unless you're using Vista. XP 64 was not very good.