Comment 28 for bug 63558

If vga=791 doesn't work for you, have you tried other values?

You can try one of the following, and see what happens:

vga=758 (640x480 16bpp)
vga=788 (800x600 16bpp)

See more vga modes here: http://www.ubuntuforums.org/showthread.php?p=1541970

You should edit /etc/usplash.conf to change it to the same resolution as the vga mode passed to the kernel, and then:

sudo update-initramfs -u -k `uname -r`