You can read about the Sempron here;http://www6.tomshardware.com/cpu/20040728/index.html
Basically the Sempron is the pretty much the same as some models of the Athlon XP with 256k L2 cache and running on a 333 MHz. FSB.
The Athlon XP supports anywhere from 266 to 400 MHz. FSB and either 256k to 512k cache depending on which model you buy.
700 Mflops in SETI!