The Semperon is a 333mhz bus, but get the 400Mhz Ram, 'cos then you can upgrade to a full Athlon at 400mhz, which are steadily increasing over the 2.1 Ghz stage. Your motherboard should support it. The memory itself will downgrade to the lower bus settings, without issues. I was doing the same thing, until I upgraded to a 2.2 Barton. :-D
