I don't think it's hardware compatibility.

I used a Dimension 2400 (1 GB RAM) as my primary desktop for several years.
It's not an ideal Ubuntu platform: the ancient Intel Integrated Graphics chipset
is poorly supported in newer Linux kernels. Ubuntu 8.04 was rock-solid, but
8.10, 9.04, 9.10, and 10.04 were either unbootable, or crashed frequently.

10.10 was rock-solid. I didn't install 11.04, but the live CD seemed OK. (I've
since retired the machine.)

I never had any problems that remotely resembled the ones you report. Take that
for what it's worth. How's your RAM?