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Shuten.
Both systems will be fast so in the end it comes down to what you're comfortable with and what your abilities are. If keeping a budget is the priority, you'll be able to get more for you buck going the AMD route, but the P4 with DDR looks excellent especially with the SiS board sporting DDR333 support. Here's what I would get for the budget minded/P4 minded. I'll use $600 in both cases and you can see how far the money goes...
--Budget--
Athlon XP 1600+............................$130
VANTEC CCK6035D copper HS.......$21
Shuttle AK31 Rev. 3.......................$80
256MB Crucial PC2100...................$61
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Total: $292
--Intel Route--
Intel P4 1700 478 Pin Retail.....$204
ECS SiS645 P4 DDR board........$88
256MB Crucial PC2100.............$61
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Total: $353
In both these cases I've used a "budget" board that will be both inexpensive and stable. As you can see, the prices are close, but may make the difference between a GF 2 Ti and a GF 3 Ti200, or a 350watt PS and a 431watt PS. Generally, the Athlon 1600+ will outperform the P4 1700Ghz by up to 10% or so, but this will depend on application, and may or may not be noticeable. The heatsink I chose for the XP is loud (Delta fan) and a cheaper $12 one can be used if you don't plan to overclock much. Hope this helps. Good luck!
Oh yeah,
here's a review of the DDR based Intel chipset.
And
another.