ATM I don't know of any review page I can point you to, but basically a Sempron 2400+ is an Athlon 2000+ but with an FSB of 333 instead of 266. They have the same cache memory and operate at the same clock speed, but whereas the Athlon XP 2000+ runs at 133x12.5 = 1666 MHz, the Sempron 2400+ runs at 166x10 = 1666 MHz.
Recently I ran a mini-test of my own, comparing the two processors with everything alse equal. The test was auto-routing some PCB designs of varying complexity. The result was a dead heat, i.e., they finished all the tests in exactly the same time.
Benchmarks scores may be different for different applications. The higher FSB speed of the Sempron may produce a slightly higher score for some apps.