In recent months, I have been running Sun's Virtualbox software to run multiple guest operating systems. One of my two monitors is an HP LP3065 30" LCD, which has a 2560x1600 resolution (4 million pixels).
Virtualbox has a very nice feature which allows the desktop to be resized up to the host's resolution. In theory. When I tried to use the feature, I noticed that the guest couldn't be maximized. The reason turned out to be that the default video memory in Virtualbox was insufficient. 2560x1600 at 32 bit color depth requires 16384000 bytes of video memory. Once I increased the video memory to 16MB, I was able to maximize the guest OS window to fill up the entire screen.