The P4 2.4C or 2.6C with 800FSB will give you the best performance for the price compared to the 533FSB versions. Either go with an Abit or Asus motherboard using the Intel 865 or 875 chipsets. As far as memory goes make sure you get 2 sticks of PC3200 DDR (or higher if you want to get better ocerclocking performance).
I'm going to have to recommend an Athlon 64 3200+, simply because if I don't there might be a riot.
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But seriously, I'm backing up TTZX suggestions with a couple of minor qualifications. Don't bother with 875 unless you actually <i>need</i> features that it offers. The awe-inspiring PAT isn't really awe-inspiring at all.
I'd say look at the <b>865PE</b>. (PE is important because you want official 800MHz FSB support.) I'm not so sure if Asus or Abit is vital, but there <i>are</i> plenty of motherboard reviews out there (including some at THG) so just make sure to research your mobo before you buy.