the k7s5a is over a year old... in my opinion its not a good choice for upgrade (hehe although i know many would disagree with me 🙂 )
if you absolutly have to keep your pc133 ram then the k7s5a is probably your best choice
but running the new athlonXP cpu's with pc133 really cuts down performance... the athlonXP requires much more memory bandwidth then the older athlons did, so expect a big performance hit
if at all possible sell your pc133 in the fs/ft forum and buy some ddr and use it with a new motherboard (something like the kt333 based epox 8k3a)
**edit**
actually if you want usb 2.0 then the 8k3a probably isnt the best choice (since its doesnt have the new usb standard)
the gigabyte kt333 board has the new usb, so does the MSI, chaintech, soyo, abit, and asus