I just ran across an interesting article on Win2k multimonitor support. Excerpt is below. Here is the link:
http://www.realtimesoft.com/multimon/faq.asp#TrueMultimon. I'm not sure how current the article is -- could be more cards have true multimonitor support now.
Due to a limitation in Windows 2000, dualhead cards that use a single chipset to drive both monitors require special workarounds in the driver to be properly recognized by the system. If these workarounds are not implemented, Windows 2000 sees a single large monitor instead of two.
This causes the following problems:
1. using different resolutions for each monitor is not possible
2. windows are maximized to the desktop instead of the monitor they are on, and dialog boxes appear centered on the desktop, split across monitors. Software included with the card may be used to work around these problems though
taskbar is extended across both monitors instead of only a single one. Nvidia's desktop manager fixes this problem
3. multi-monitor software will not work properly
The latest drivers from Appian and Matrox have full Windows 2000 multi-monitor support for the following dualhead cards:
Appian Hurricane
Matrox G400/G450/G550
The following cards don't have drivers which implement the necessary workarounds, and so exhibit the problems mentioned above:
Appian Gemini
ATI RADEON VE
cards using Nvidia chipsets with TwinView