There's nothing wrong with the pentium architecture. Infact in the middle of Netburst's lifetime a few years ago (after Willamette, before Prescott) the Northwoods were definately some of the best chips around and great clockers. The Pentium D may be based on this outdated Netburst architecture, but they're still very capable chips especially at the prices Intel has had them at for the last few months. However, with Core 2 Duo I don't know why anyone would really want one other than just to get a decent processor very cheap, which in that case I'd recommend a single core Athlon 64...
I would have gotten a single harddrive for your system. RAID 0 can be nice sometimes when you need a ton of storage and then two drives are cheaper than one (2x 250GB opposed to 1x500GB), or that combined space wouldn't be available at the time (2x500GB = 1TB which doesn't exist yet.) However this RAID setup falls into neither category. btw 160GB drives and 320GB drives are very common.
2GB RAM is great
Never heard of the 7900 GS, but I'm sure it's a great card
If you really like or need the Xi-Fi, have fun with it. I would rather spend the money elsewhere, like in this case exchanging the current processor/mobo with a Core 2 Duo mobo and processor.
19" screen is meh. For gaming 5:4 isn't too good. If that's a widescreen, 19" LCD widescreen has a weird resolution (it's widescreen, but you can't really fit two documents on both sides, too much to natively display 720p, not enough to display 1080p...) and may be a bit inadequate when you got a 7900 series video card.
While it may not be exactly what I'd order, I still think it's a fine system!