Ubuntu 64-Bit Problems - Post-Install

I just installed Ubuntu 64-bit version and the install went smooth as smooth can be, but when I try to log on I type my username/password and it passes that screen and then there's a white "blotch" in the middle of my screen. Nothing responds and I restart but it still doesn't work. I've read somewhere in the Ubuntu forums that the 7800GT isn't supported with Ubuntu, so should I uninstall? And how would I do so?