Strange boot and resolution problem in Ubuntu (Dell)

When I tried to boot into Ubuntu on the Dell this morning, it just kept going back to the login screen.
I found another blog post that seemed to have had a similar problem and overcame it by deleting ~/.gnome, .gnome2. .gconf, .gconfd and .metacity. However, when I did the same, no improvement.
So, now I had to re-install Ubuntu Hardy without formatting the /home.
This went fine and I got everything back (Opera, yakuake, /etc/dhcp3/dhclient.conf etc, etc).
I also had to manually install the legacy nVidia driver 96.43.05 and this went fine. When I restarted X, the screen came back with the required 1280x1024 resolution and everything looked good.
So after a while I rebooted, but to my great surprise, the screen came up saying that it was in Low-Graphics mode (800x600). So, I re-installed the nVidia driver. The installer said the driver was already there but would be deleted in the new install. Once again, when X was restarted everything was fine but on a further reboot got the same problem over again.
Interestingly, the old xorg.conf file which the nVidia installer renames as a backup, has some differences from the new file. I really have no idea how it gets changed but, even so, I don't see anything that should lead to a 800x600 resolution.
Really don't understand this. Wonder is it at all related to the boot problem I had this morning which, equally, has not been explained.