Hey Gavin. You can get a usb video adapter for around $100 from Tech Pacific not the flashiest for animations (although will play things better than I expected for USB my first reaction was yeah right) slightly more cpu load while doing animations from youtube. No good for gaming I would say.
For general office work such as viewing websites, word documents etc.. then I wouldn't expect anyone to notice the difference between the display on the USB graphics and normal DVI.
If you want me to find the model I'll get it for you on Monday when back in the office.