Well, unlike some of the other posters, I actually read and re-read your description and wanted to hit you with a couple of questions.
1) You mention gaming and XP in the same post. I love my XP, but I'm hearing from some of my gamer customers that they like having thier Windows 98 Boot disks around for playing games not supported under XP. You may want to keep that in mind. I have a good hack for running no-cd Diablo II and LOD under XP and it works great (even if it did move my SAVE folder to under my personal profile. I guess XP was worried that someone else would log in and try to use my characters, god forbid).
2) If you are going into dreamweaver, adobe or other multi-thread supported software, I would highly recommend a motherboard with DUAL CPU's, even if you only use 1 of them initially. In this case, I would stick strictly to an AMD chipset for performance and stability. I can't speak for everyone in the group, but when I'm compiling, I love the performance gain of the dual cpu configuration. Of course in a dual CPU config, you can forget about running Windows 98. My question here is how much compiling or rendering are you doing compared to other things?
As for your dual screen scenario, I would look to a product that can really leverage your AGP bus and my personal opinion is the ATI card with a Radeon just isn't it. Reading up on Tom's tests results here will give you a better indication and some side by side comparisons. I would probably go with the Matrox card since many gamer and programmer customers alike have been raving about it, not just in terms of price, but rather video quality and performance.
In summary, if you are a serious web programmer or data compiler, you are really going to want the dual CPU option, even if you don't use it from day 1. If you are doing split screen dual panel, you are going to want a video card that has the horse power to let you multitask without sacrificing performance or video quality.
Just my two cents.
Steve Benoit
Stable Technologies
'The way IT should be!'