Yeah, I would avoid SLI at the moment. That area is just not mature enough to be worth the pricetag. PCI-Express is a bit more seasoned, but still is not the official norm of the community yet. But for PCI-E, there are cards from all the major vendors. Most are the high-end, but there are some mid-level cards as well. If this is a gaming rig, follow these rough guidelines:
1) At least 1G Dual-DDR RAM.
2) Decent CPU. Doesn't have to be top, but should be up there.
3) At least a 2 drive RAID-0 PATA/SATA setup. If the budget allows, go with Raptor IDE drives from WD
4) Decent MB chipset. Don't go with a last year model style. The Nforce 3 and other Intel chipsets as pdb just pointed out are good..
5) Do not use onboard sound. Get a Creative or Turtle Beach PCI card. Most onboard (not all) are not adequate for a gamer since it eats up CPU cycles. Again, some newer chipsets take care of this problem.
6) Spend the rest on the video card. Seriously, if they are dead set on a top gaming rig, then $400-$600 bucks on a video card is not out of the question.
Research on the gaming websites and be sure to pay
Toms Hardware a visit.