Scrytch: you might try the following procedure to set the display resolution and refresh rate in Ubuntu:
Read this FAQ on display resolution/refresh rate at Ubuntu:
http://www.ubuntuforums.org/showthread.php?t=83973&highlight=configure+display
I had success with the following:
1) run from terminal: sudo dpkg-reconfigure xserver-xorg
2) accept all of the defaults until you get to resolution.
3) pick only the recolution you want (1280x800 on a MacBook)
4) use the advance settings to set the referesh rate; I serached around on the Parallels forums and found a post with MacBook Pro settings of horizontal: 30 - 82 kHz
vertical: 40 - 120Hz (see this post here:
http://forums.parallels.com/showthread.php?t=249&highlight=solaris)
5) accept the defaults there after and restart
FWIW, I tried editing the xorg.conf file, but I could not get the settings to stick. For some reason, it just wouldn't work, so I gave up and ran the Linux program designed for tweaking the xorg file. (If you edit the xorg.conf file, I think you have to reboot, not simply start Gnome again.)
Good luck!
PS Be sure to back up your Ubuntu hard disk before you start messing with things. I learned the hard way. Got it so messed up had to reinstall.

Now I always keep a backup copy of the HD file before I start hacking around. Cheers.