When i was looking to upgrade but keep my old SDRAM about 6 months ago, the choice was between the ECS K7S5A and the shuttle AK32 series. I got the K7S5A cos it was cheaper (although they are both around $55 now)
I read all the advice on the K7S5a being picky, and tricky to work with, and... they were right. I've had a short series of little problems, culminating in a complete inability to find an internal modem that won't stop my pc POSTing. (but i'm using a serial one now, and appreciating the difference). Nothing I couldn't work my way around, but its been a bit of a pain, and now i'm wondering if i should have just spent the extra money. Plus you'll need a good Power supply with this motherboard. It is *very* fussy in this respecy. decent 300W minimum for an athlon or XP. 350 or 400 pref.
I havent used the shuttle myself. but i have heard its more reliable, and a bit more user friendly. Both accept SDRAM or DDR, both'll take up to XP CPUs, both have onboard sound.
I don't know about the shuttle, but the K7S5A is definately not an overclockers board. Its possible, with special oc bioses, but lets just say its not the overclockers ideal.
I think the reason i didnt choose the shuttle was because its only a KT266 chipset and the K7S5A's SIS 735 is supposed to be faster. But looking back, maybe i should have made the other choice.
Actually, if i did it again, i'd just sod it and buy a more expensive MB, since i ended up getting the DDR anyway!
sorry about the rambling, and hope this helps some - check out
Newegg for more details.
good luck!