PC2700 is only supported by future chipsets. I'm not sure if you could use it for overclocking, but there's not really any point.
PC2400 is really only for overclockers. It'll help you get above the normal 133 FSB.
PC2100 is the standard memory type. If you're not overclocking, get this.
I always recommend <A HREF="http://www.crucial.com" target="_new">Crucial</A> for memory, because it's high quality and their service is excellent. Other good memory is Kingmax, Corsair, Mushkin and OCZ.
<font color=green>I post so you don't have to!
9/11 - RIP</font color=green>