Hi,
I had problems with multimonitor support, especially connecting the plasma monitor to my laptop vga output.

It would work while booting, but when windows loaded it did not work any more!
Also, it seems FN + F5 no longer works, while in Vista.

Anyhow, I got it working by doing this:
Right click on the desktop, choose: "Personalize".

When the dialog opens, you see in the left column: "Connect to a projector or other external display".

When this opens another dialog, there will be a button: "Connect display".

This sometimes opens another dialog where you can choose if you wish to clone, span, which direction, etc. Hope it helps! Good luck!