I am running beta 6 fullscreen on a monitor connected to a Macbook Pro. When in that mode, if I open the About menu option from Parallels, the popup seems to appear behind the fullscreen display so I never see it. Also, I lose control of the guest OS until I manage to close the About window (I think ESC did it after I clicked the Parallels icon in the Dock). Another problem when running fullscreen on a second monitor is that the mouse tracking doesn't seem to recognize when I leave the Parallels window. I essentially lose my mouse when I move it back to the Macbook LCD. If I task switch (CMD-Tab) to another running app I get the mouse back. Also, I can use CTRL-ALT to release the mouse after I have moved the mouse back to the built-in LCD but it all feels a little clumsy. Finally, mouse tracking seems to lag a bit in fullscreen. I didn't notice it as much when running fullscreen on the built-in LCD. My external monitor runs at 1280X1024.
I am running beta 6 fullscreen on a second monitor 23" Apple resolution 1600 x 1000 without any problem, same for the mouse tracking. Have you updated the Parallels Tools ? Phil Mac Book Pro 2Go
I have updated Parallels tools. To confirm: You do not have the About box display issue? Are you saying that the mouse tracking detects when you move from the Parallels screen to your internal LCD?