I did dualie monitors/displays for years!! it was a breeze when win98se came along!
I actually bought a matched pair of S3/Virge 3d 4 meg PCI Cards about 3 years ago, just for it!
You can do a lot more work w/two displays, some programs have built in/native support for it (Illustrator 7 & Up), more screenspace means a lot less flipping back and forth between windows, more pallates/windows/toolboxes can stay open, and it really impresses friends!!