It depends on how much performance you're looking for. You'll get more power out of the 800 fsb, but the cpu will be a little more expensive, as will the pc3200 ram. If you're not worried about max performance, then a 533 intel or 333 amd should be fine for you. A 2.4 P4 northwood with an 800 fsb goes for somewhere in the neighborhood of 160, but you could probably get a 2.8 for 10 - 15 more. The barton xp 2800 will only cost about 120, but also has 333 fsb. The 2.4 prescott goes for about 120 and the 2.4 northwood is about 130, both with a 533 fsb. (a 533 fsb is intel marketing talk for a 166 mhz fsb, same as the amd 333 fsb). I have heard things about the prescotts running hot, so if you're planning on overclocking you might want to look into that.
You should take a look on tom's or anandtech for some cpu benchmark tables. that will give you an idea of how they compare.