one thing i learnt with ubuntu is that during
installation if one makes an error and goes back a screen it seems to
upset things. I had someone on another group who has update problems
with 8.04 - i don't. I did have update problems with 7.10 when i
installed another desktop environment and then removed it. Shouldn't
have given trouble but did - somewhere there was a glitch.

I don't think it is an installation problem - some glitch that isn't
probably worth wasting time and effort on to be honest. Another
installation is a solution but that goes without saying - i know "it
goes against the grain" but saves you less time in the end. See if you
get the same problem or try ubuntu. I had trouble with another distro
on the same machine that ran ubuntu perfectly and loads of problems.
I've got three machines and each one runs ubuntu fine.