just get the P4S533...it has the updated sis645dx chipset, 533 FSB support and "unofficial" ddr400 (pc3200) support...the P4S333 does not support the 533 FSB (unless you overclock) nor ddr400 (again...unless you overclock)...
and both motherboards have support for 3.3v video cards (ie. your voodoo 5 will work on those motherboards)...
on both motherboards...the P4 1.6A will overclock to at least 2.1 ghz (133 FSB)...
if you need more info....go to <A HREF="http://www.asusboards.com/forums" target="_new">asusboards.com</A> and go to the "other chipset" forum under intel chipsets....there are many people there with experience with both the P4S333 and the P4S533.
<b><font color=red>ATI</font color=red>'s drivers are like a broken faucet, they both keep on leaking...</b>