Several things to consider here.
Upgrade Path: Many people have posted that Intel is a safer upgrade path, however, I'd like to point out that Barton will still be socket A and while next gen P4 is supposed to be Socket 478, Intel has changed it's socket frequently in the past. I'd be warry of getting an Intel board and expecting to be able to put a next gen chip in it at a later date. Even the P4 changed sockets only a few months after it was released. Doesn't seem like a very safe upgrade path to me. But I suppose Intel could continue to use Socket 478, I'm just saying nothing is for sure. And Hammer will not be socket A, but I think both platforms will continue to be used for quite some time with the P4 ramping up and Barton.
Speed: The 2.26 P4 will be faster at most apps than the Athlon XP 2000, however it will cost significantly more $274 vs $160. To do a fair comparison, you should compare the XP 2200 which will be very close to the P4 is most benchmarks, and in real world performance I doubt you'd notice the difference. If you are planning on overclocking, the P4 will have an advantage. But remember that overclocking doesn't always work. As far as Intel having the performance crown or not, that doesn't really matter unless you're buying the fastest P4 (which your not). Unless you care about being on the "winning side", I don't think it matters much.
Heat: Fast P4's put out a lot of heat too, their stock heatsinks are just better than Athlon XP stock heatsinks. I guess Intel does win here, I'll admit they have a better cooling solution. But I have an Athlon XP 1800 with a low-flow Panaflo fan (14 cfm, 21dba) and a copper heatsink that does just fine with a few low-flow Panaflo case fans. My case is super quiet (except for my GeForce 4 which I'm working on). Despite what people say, building a quiet AMD system that still is cool is not difficult at all.
Bottom line. As most professional reviewers and analysts have said, either is a great choice. Neither has a substantial lead over the other, so it's really a matter of preference. If you want to save a couple of bucks and don't mind having to take extra care putting on your heatsink, go with AMD. If you want good overclocking and the piece of mind of an Intel system (even if I think that's silly, it's your money and piece of mind can never be overrated), go with Intel. Really, you will be happy with either an AMD or an Intel system.