Very easy to do with the 8800GT. Just Plug in 2 montitors to your card and restart you computer, it will most likely find two montiors and open a wizard to set it up, if not you just go into the video card setting and set it up manually.
Its worth it when you need 2 workspaces for things like video/photo editing or running things like Sonar/Pro tools/Cubase for the extra room. I usually just use one display, but when I'm Running Sonar for recording, I use 2 (and old CRT) and open all the plugin widows and setting in the CRT. Makes life so much easier