After installing a Graphical interface in order to be able to use gnuplot I was not able to use the mouse ... the mouse was there but I was not able to control it :(
I found the solution here
At boot press the Esc key enter the grub menu screen.
Make sure your kernel boot line is selected.
Press e to edit the kernel boot line.
Type i8042.noloop at the end of the line.
Press enter to accept the changes and then Publish Postb to boot.
Once logged into Ubuntu, open the /boot/grub/menu.lst as root.
Add i8042.noloop to the end of the kernel boot lines.
The article also explains how to solve Graphic problems with the display and the color depth with Ubunto desktop in Virtual Pc 2007.