This system should last you a long, long time, if you're not the type of person that gets too excited about new upcoming technology like Socket M2, new dual cores, DDR2 SDRAM, DDR3 SDRAM, GDDR4, third generation SATA, PCI-e second generation, and so on. You can always upgrade piece by piece when the time comes, but I'm afraid the motherboard now will undergo quite a massive change in the next few years. I can bet on that.
I estimate at least $2500 + for your system. It's still WAY cheaper than buying a pure gaming machine retail. So that will give a big boost of confidence.
That BFG 7800GTX is a super nice video card. I like eVGA too. For the power supply, I like this one:
Weekend Sale, Ends 11/14/05
Antec TruePower 2.0 TP2-550 EPS12V ATX12V 550W Power Supply 115/230 V UL, TUV, CB, FCC CLASS B, CUL - Retail
Oh yeah, and it's on sale right now too. I'm in love with that power supply, drool-give me some juice. Nvidia SLi certified too.