Yes, you can. Windows XP makes it super easy to perform this function. I did it on my old video card. My friend was doing a HUGE project that was using Adobe something. HUGE 12' poster items. I let her use my computer since I was running a faster computer then her. I stole her PCI video card and monitor, installed it on my system that was running a single output Matrox at the time and it worked so sweet. I was even able to do with three monitors when I got my Radeon 9700Pro Dual out and took her video card and monitor.
If you are trying to run two monitors, I suggest getting a dual output video card first (it's a very common thing these days). They are a lot faster and simplier to setup overall since it is only one video card and only one video driver.
Happy multi-monitoring!