If you’re decided to take the plunge and buy a bunch of parts to build a new computer system, good for you! It’s the only sane way to get the best PC out there. Just keep in mind that SLI != Crossfire, and that your choice of motherboard has consequences in what kind of video card setup will work for you. I have a commercial account with my parts provider and my rep was able to straighten things out quickly, but it’s still best to avoid making the mistake in the first place!