Sure you can get 2 cards but they will get outdated fast and later won't give you the performance you want. One 7800GTX will give you the performance you want now and later in another year, you can drop another GTX. Make sure you have an SLI ready motherboard. Also wait for newer motherboards to come out because newer motherboards will use true "dual x16 slots" for SLI gaming. Previous SLI boards divided the 2 x16 slots into 2 x8 slots. With this newer motherboard, you will twice as fast FPS as regular SLI gaming. This might be a bit confusing but google in Asus A8N-32 Deluxe and read up the reviews on it and see the new technology it incorporates. Rememeber I suggest you get one $500 7800GTX.
I am building a new system and I would like to know yalls advise. Should I get two video cards priced around 200-250 or get one more powerful one costing 450-500. Anyone know which configeration would be best for gaming?