XP Pro is no longer available from retailers, although there are still
old copies lying around.
As long as you plan on using XP Pro on just one PC without ever
transferring it to another PC, the Retail version (which permits you
to transfer by the license) is totally unnecessary. The Generic OEM
version (which can only be used on one PC, period) makes a whole lot
more sense. The only difference between Retail and generic OEM (also
known as System Builder's) is the license and price. That's it. New
Egg sells the current OEM version of XP Pro:
http://www.newegg.com/Product/Product.aspx?Item=N82E16832116515
Sixty dollars cheaper than what you found!
Furthermore, most home users don't need anything more than XP Home
(which is almost identical anyway to XP Pro). Here is the link for XP
Home:
http://www.newegg.com/Product/Product.aspx?Item=N82E16832116511
$89.99.
Finally. You may not have to purchase a disk at all! The reason: you
*still* have a license to run XP on that PC; there is no reason to
purchase another license!
In your first post, you stated, "I heard you can borrow a disc for
that ("that" meaning performing a clean or repair install)." That is
absolutley correct. You just need to make sure it matches what you
have (which admittedly may not be that easy to find, depending on
your circle of acquaintenances): a generic OEM CD of XP Home,
preferably at SP3 (but earlier service packs would work too; but you
would need some guidance if you plan on performing a repair install.
However a Clean Install would present no problems with regard to SP
level.). Just make sure you use the product key that is on the
Certificate of Authenticity sticker on your PC if you borrow a CD (in
the event that doesn't work you would need to use the generic master
key provided by the PC manufacturer, easily determined by a Google
search). If you purchase a CD, you might as well use the product key
that comes with it.