Dan´s Data has posted a guide to building an all-purpose PC. Here a snippet:

A 500MHz Celeron has roughly half of the processing power of an 800MHz P-III, but the faster processor costs five times as much. Assuming you can find one, of course; thanks to manufacturing shortfalls, Intel CPUs faster than 700MHz pretty much don´t exist in the retail channel at the moment. But there ain´t no shortage of Celerons.

Check it out