This might sound odd, but I have a very peculiar graphics driver issue. Basically, I pop the Live CD in, and "try Ubuntu". Everything works fine from GUI animation, to fullscreen flash, to even full-screen 3D graphics.

However, when I install the OS itself, and reboot into it "properly" for the first time, everything breaks. If I stick with open source, I'm unable to use the computer at all, and if I switch to any of the proprietary ATI drivers, usually the OS will be laggy, full-screen flash videos will be black, or 3D graphics will be choppy and glitchy.

It seems as if somewhere in between testing the OS out, and installing/updating it "breaks" the drivers. What can I do to keep them?

I have an ATI Radeon HD 6850 (1GB) graphics card, and I'm running a 64-bit OS.