I haven't tried the new Ubuntu yet, but I have managed to get a fairly stable version of Debian Squeeze onto this machine.
I installed Debian Squeeze from the stable DVD
without many problems. As soon as I tried to do the initial update the system froze with the now all-to-familiar "fuzzy screen freeze".
On the subsequent reboot I appended acpi=off to the boot line and managed to do the rest of the updates.
There are only a few issues with the system as of right now:
It's using kernel version 2.6.32-5-686 (an older kernel, but the most current in Debian Squeeze stable)
The audio hardware was detected on first install and then I lost it after a few updates. It took a while to realize that I only have audio after a full power-cycle shutdown. If I reboot without power-cycling, I lose the audio hardware. This is so far unresolved.
I had to download the wifi driver from realtek (making sure to get the version for the earlier kernel version), but a "make", "make install" and a reboot later - wifi was fine.
I'm stuck with 1024x768 resolution. I tried to apt-get install the fglrx modules, but all I achieved was the only "fuzzy screen freeze" I've had since the initial install.
Not all the function keys work. Notably the enable/disable touchpad hotkey (FN-F9). (I hate when my palm touches the touchpad while I'm typing and throws the cursor off to some random part of the screen in the middle of a sentence...) Volume and Brightness seem OK though.
I'm still testing things but so far everything else seems fine. This isn't a solution, really, seeing as this machine should be capable of much better video, but at least I do have a linux working and apparently stable, so far.
I would be interested in hearing if anyone has any luck with the new Ubuntu.