Wow, never mind. I'm behind the times. I see now that PCI-E x 1 slots are definitely not compatible with the type of graphics cards I would want to put in.
I'm returning the PC I bought, and, looking at the rest of the line-up at this place, none of them have 2x PCI-E x 16 slots.
Guess I'll be building from scratch. And given that I don't want to buy a new copy of Vista and then pay for the upgrade to Windows 7 (one of the things that sold me on the machine I bought yesterday was the fact that @ $360 it came with Vista 64-bit and a free upgrade to 7 when it comes out), I won't be building my own machine until October. Try as I might, I can't spec out a decent rig for the same price as I paid for the one I got yesterday. If I wasn't so attached to my 3 monitors (and dreaming of a 4th), it wouldn't be a problem.
Thanks for your insights. You saved me money and a lot of headache.