Alright, its unfair to discount apple as you have. I am a PC user, and currently have an Athlon 4 1.4 gHz, and it just screams, and I love it. BUT, Apples are great for what they do best. First of all, windows is a very unstable OS compared to OS 10, and this is coming from a Windows user!!! Why do you think Macs are used in all hollywood studios, magazines and newspapers for editing? They are better for multimedia, the OS is much less bulky and cartoony, and are suited towards this application. For trading, a PC is a much better choice as compatibiolity with products is an issue. The dual G4 processor setup can rival most Pentium 4 systems (which in fact are not much faster thatn P3s...mostly a marketing gimmick). Search on Google for G4 vs Athlon vs. Pentium, and you will get some cool comparisons.
Apple has been experimenting with Athlons, and has considered putting in a dual Athlon configuration in an Apple. This would make it hands down the sickest computer ever built. I like my PC, I like XP, and I love Athlons. And PCs are better for trading, but not for multimedia, graphics or programming.
BTW I have run Windows XP on a G4 quite successfully a number of times, and its pretty damn fast....faster than my old P3 anyways....