I just picked up a PNY NVIDIA GeForce 8500 GT PCI Express x16 video card for $60 at buy.com. It has 512 MB of memory, a DVI port, and a VGA port and allows you to run two monitors under Ubuntu 8.04 just fine.

You can either download the restricted nvidia driver from the Ubuntu repositories, or manually download the latest driver from Nvidia’s web site.

You can set it up so that both monitors act as one large desktop, or each monitor as its own X-Server screen by running nvidia-settings.

Do you learn better by watching something rather than reading? If so, then maybe this site is for you. They provide many HOWTO videos for Ubuntu.
Ubuntu Screencasts