I have 2 CRTs on my home system, with a single video card. My ATI Radeon has 2 outputs, one for a digital TV, but they include an adapter to allow CRTs. I couldn’t actually use it until I upgraded the power supply in my system, but it is nice to have it working now. Of course, now I want to upgrade the old 15" monitor that is my second to something that is larger and more versatile. 
On a similar note, you can run x2x, x2vnc, win2vnc, or one of many similar programs, and control two (or more) computers with the same keyboard and mouse.
Also very cool.
Just to clarify from the earlier posts - yes, if your video card doesn’t have dual-monitor support, you need a second one. And of course, it has to be a PCI card, because there’s only one AGP slot. And also try to get a matching chipset, to minimise the chance of problems. So it might be easier to get a new card with dual heads. Either way, yes, you can adjust them easily within Windows via display properties - and often the bundled software with the card will give extra utilities.