Just to be on the safe side. I might be installing a video card for someone but I have never done this before. I have read about it a bit and if I read right all I need to do is put the video card (AGP or PCI-E) in the slot and boot up and the Mobo should reconize it then log into windows and install the drivers??

Does anyone know of anything I should watch out for?

Make sure you plug the power in, too, if it needs power from the PSU (the new cards do, and mine has screeched at me when I forgot that). The mobo should recgonize it, and windows should display, but you will need to go to the manufacturer web site and download the latest drivers to get full use of the card.

When my computer has no video driver installed, it runs 800x600 at 60Hz, and makes the CPU process the graphics, too.

Yeah thats pretty much it. Just don't touch the connections on the bottom of the card (the part that goes into the slot). Plug the monitor cable into the card; if at boot up you get no picture, you will need to reboot it with the plug in the motherboard video port (if the motherboard has onboard graphics). Access the BIOS and switch off the on board graphics, then save, exit and shutdown. Plug the cable back into the new video card and the picture will come up.
Either way, once you have the picture up, all you need to do is install the video card drivers. (Use the autoload from the video card drivers CD, as opposed to the windows automatic one). Then you're good as gold!

Oh yeah, what Landscader said as well (if it needs power)

Make sure you follow safe handling techniques. Leave it in the grounding bag until you're ready to install it. Then wear a grounding wrist strap or at least touch the metal side of the case before handling the card or touching anything inside of it. You can easily fry any electronic part with the static electricity in your body. When you walk across a carpet in the dark and see a spark leap from your fingers to the doorknob, that's possibly 30,000 volts. It only takes 30 volts to destroy electronics.

Ok thanks for the quick reply