I have opened up this question on launchpad too, but in the interest of getting a bigger response base I am posting it here, hoping someone will pick it up.
Natty doesn't behave very well with the Intel 82845GL chipset. I booted my old machine with Natty today to test drive it. The specs are:
Processor: Celeron 2.4GHz Video: Intel 845GL RAM: 1GB
The first problem is that the display is borked! What do I mean? Well, see for yourself:
If that gets fixed (and it did for a while but is back now), Unity is disabled.
I think these issues are owed to hardware acceleration being disabled...or in other words not the right driver for my hardware. A google search on 'intel 82845GL ubuntu' does return other users having similar problems in the past but I haven't been able to pick out a solution in the many many discussions on the subject- partly owed to my 'linux naivety' I guess...but maybe you can help?