I just upgraded a month ago. Core 2 Duo E6600, 8800GTX, and 520GB RAID-0.
I was considering 8800GTS too but at the time, there was just $150 difference between GTS and GTX. And the performance difference was well worth it for me. And I'm looking to go SLI in about a year and by that time, there'd be very little price difference between GTS and GTX. But GTX SLI would be substantially more powerful than GTS SLI.
And what RAID-0 does for games is loading times, installation times, and faster file transfers under Windows. But even if there is no frame rate gain in games from RAID, why not go RAID? It's not like you have to purchase expensive SCSI controllers like we used to. With today's motherboards, RAID controller comes with it and RAID-0 doesn't decrease hard drive capacity like RAID-1. Buy two smaller drives rather than one big one. Yea two smaller drives will be more expensive but not much. In 500GB setup, two 250GB drive may be $10 more than one 500GB.
Some people tells me "yea but in RAID-0, if you lose one drive, you lose all data". Well... that's same for single hard drive. It's actually better with RAID because if one drive goes bad, I can still use the other for single drive setup. Whereas with one large drive setup, if it goes bad, you have to buy another.
And for motherboards, make sure the motherboard is Intel Quad Core ready. Nowdays with cheap CPU prices and really high GPU price, you tend to upgrade your CPU before the GPU. And I'm a believer that multi-threading in gaming will pull itself together soon.
Finally, compare prices between Newegg.com and ZipZoomFly.com. Some components, newegg is cheaper and some are cheaper on ZZF. And ZZF has free shipping on everything so consider the shipping price from Newegg. I bought half the components from newegg and half from ZZF.
Make sure you purchase Vista OEM when you purchase the hardwares if you're planning to go Vista. OEM is cheaper than Upgrades.