this board does not really like to be overclocked, I never had any luck and the friends who had it did not do well either. As for what cpu's it works with... it can go up to 133 fsb (266 effective due to DDR). This means any of the durons (I believe) and any of the original Athlons and Athlon XP's with the palamino core will work on it. Anything above 133 bus (the T-bred and barton) will not work on this board.
That being said you can get a cheap xp1700-2400+ for this board, all of which will work on it. It can take DDR ram up to DDR266 (well, it can take higher, it just won't run at that speed) One nice thing about the board is that it can take a fsb 100 cpu and 133 DDR ram or SDRAM and you can run them independantly. ie, you can have the CPU at 100fsb and the ram at 133/266. This makes a nice option if you want to get a really cheap old Athlon Thunderbird (they go up to 1.4ghz)
I would find a soundcard as the onboard sound sucks, but the onboard lan works wonderfully. One thing should be noted, I got the first version of the K7S5A (old rev 1.0) when it came out, so my specs can be a bit off. For instance I hear the new board has USB 2.0 where mine did not. I am not sure if the sound was changed on the new version but mine sucked, get a cheap SBlive value for decent but not too pricey sound.
Oh, you can use pretty much any vid car with it, but the AGP only goes up to 4x. Also the slot is not a pro, so don't try to use those rare agp pro only vid cards. I ran an old Radeon LE up to a Radeon 8500 on the board with no problems. You can get a low price Radeon or a GeForce 4/FX for under $100 if you want a good budget cards, just stay away from the 7000 series Radeons and the MX versions of the GeForce, they are not worth the money as faster solutions can be found for less.
hope that helps
-spike
EDIT I am not so sure about the processor cores, all I know is it can take up to a 266fsb, so don't get anything with a 333 or 400fsb. Seems that there are T-bred cpu's that are at 266fsb so I assume they will work on the board