How can I boot into Ubuntu and fix this? I get the loading bar then the equivalent of TV static. How can I get GNOME working again? GRUB is working normally and I can still boot into vista.
It's your Xorg server configuration - dump into command line and check your Xorg logs. It should provide strong clues on where the problem lie.
To dump into command line from the static screen, you can try pressing CTRL-ALT-BACKSPACE.
EDIT : CTRL-ALT-BACKSPACE was to terminate X server, not Xorg. New procedures updated below.
I have had a similar issue when installing on some machines. If choosing F4 : "Safer Graphics Mode" fixes the issue when booting from the Ubuntu CD then try setting the VESA video mode in your grub configuration /boot/grub/menu.lst file. Details on boot options can be found here https://help.ubuntu.com/community/BootOptions
Short answer: add vga=771 to the boot line. You can test this by choosing the Edit option when the grub menu appears.