XP 3000+ is slower than the 3.06ghz P4 in alot of fields, and as of current is actually more expensive than the P4 3.06Ghz in alot of places. and considering the P4 can use the same ram as an athlon that argument goes out the window. Also since your thinking about a topend machine get the Radeon 9700 or 9800(faster than fx5800 ultra).
Just my two cents from the ahaha Intel is better once more gallery.
While I think the debate between Intel and AMD is ridiculously stupid (it's always one-up-manship - how you can possibly say one company is better than the other in general, when they're constantly out doing each other?), gamefoo makes one good point - the 3000+ XP is a little more expensive. However, it seems as though the Barton core is better at overclocking than the P4, and from the benchmarks I've seen, the XP is a bit faster in some cases, and neck-in-neck w/ the Intel 3Ghz in others (Gamefoo didn't specify where he got his numbers - mine are from HardOCP). Essentially, it's a judgement call. If you've set your mind to the XP, don't let anyone else try to sway you. Be happy with what you buy.
Now, as for purchasing items, I'd look at www.pricewatch.com, www.tigerdirect.com, and the aforementioned www.newegg.com. Incidentally, NewEgg is listed at pricewatch, so it's a good indicator of how competitive their prices are compared to other companies.
Can anyone recommend me a good mobo, intel or AMD? I have a soundcard and graphics card (Audigy Platinum 1 internal and a GF4 Ti4600). I can't tell what the max processor a mobo can handle, since they often don't list it. Any recommendations would be greatly appreciated.
Best advice I can give you is to avoid cheap chipsets on motherboards. If you are buying an Athlon, get a VIA KT400 based board. If you are buying Pentium, get an Intel based board (845PE?) - whatever is the latest.
Don't buy SIS chipsets. I don't know enough about the nForce boards, other than they are used in Xboxes.