Re: Single card vs. SLI
No, go with a good, single card. SLI is very bad bang for buck option (an oft-quoted figure is 40% performance increase for 100% price increase). An 8800 GTS, 320 or 640 should easily outperform 2x 8600. The 640 version is only really an improvement over the 320 at resolutions above 1600.
The 8800GTX, 768 is even more of a beast, and the 8800GTX ultra, the top of the range at the moment.
A new card just got released, the 8800GT, which is looking like it is smaller, more powerful and cheaper than a GTS, so thats something to consider if you are looking to buy soon. There are a lot of posts flying around at the moment about this card, have a read around.
EDIT: and Welcome to the Tech Forums!