I installed a secondary monitor this week. After some failed attempts: 2 nvidia pci cards that gave me the blue screen and an agp card that disabled my on-board card, I finally bought a dual head Matrox Millennium G450 which works fine (I am only working in 2D). I am really excited about this new set-up, now, e.g., I can run my 2 consoles programs on one screen while stepping through the third one in VisualStudio. It is also nice to be able to keep the Task List on the secondary monitor.
Additionally, I installed a freeware called MultiMonitor Taskbar which extends the taskbar to the secondary monitor, a really commendable work by Roman Voska.
P.s. I am sad to say that I have uninstalled the G450 since it started giving be repeated blue-screens :( What a bummer! I have become hooked on working with two monitors.
