They're not that bad... but look at the clock speeds:
Sempron 2200+ 1.50GHz, 333FSB, 256K Cache
Athlon 1700+ 1.47GHz, 266FSB, 256K Cache
I doubt there'd be a great deal of difference between the above processors.
AMD moved the goalposts when they started naming the CPU's.
I guess it all depends on what you'll be using the PC for. Games? Video editing? or just internet/email?
Jon