Hi,
some weeks ago I asked if somebody has experience with Dual Monitors. I was unsecure if I should set up my next system with a Windows Guest, becaus dual monitors are important for me to use one windows application (Adobe GoLive).
In the meantime, I tried it out on another PC. It worked out-of-the box, so here is my report for the archives.
Host: Kubuntu 7.04, Guest: Win2K, Virtualbox 1.40. I installed a Matrox 45+. Monitors used were flat panels, one 19 inch 1280x1024, the other one 15 inch 1024x768. In KDE Setup there was offered a second monitor. I configured it as a secondary one, not as a clone, then I chose on which side of the primary monitor it should show, and re-started X. The system configured the starting resolution as 640 x 480 for security reasons but I edited xorg.conf and moved the full resolution in the first place of the line so KDE started with the full resolution.
From this moment, I could enlarge or move Linux program windows to the second monitor. The taskbar stayed at the bottom of the primary monitor and did not enlarge to the second one.
The same worked flawlessly with Win2K in Virtualbox. I could move or enlarge the Win2K window to the second monitor and move program windows as well as the tools panels only of the windows application to the second screen.
If I maximized the Virtualbox window, the Windows window or the application within windows with the rectangle icon in the upper right the program window in the second monitor it would fit exactly into it; it would not maximize to both windows. If maximized this way, it could not be moved to the secondary window. If maximized by seizing the corner with the mouse, the Windows window could be stretched to both monitors, and then any program windows or tool palettes could be moved freely from one monitor to the other.
It was, of course, not necessary to install Dual Monitors within the Windows Guest.
If a full sized program windows or the Windows window itself was moved or stretched to the second panel, it would be too high to be fully visible (and it would not scroll like a virtual window either), because the primary Monitor is 19 inch and the secondary is 15 inch. This is fine with me because I do use the main monitor for something like the main window and the second one for tools, palettes, sourcecode editor etc.