Live long and prosper. I had a similar problem after installing
8.04 which I posted before in this group. Without enabling the Nvidia
driver I had high resolution but was unable to run compiz. After
enabling the drive and rebooting I had only 640 X 480. I've neen in a
lot of forums and the #Ubuntu IRC channel for tech support. A LOT of
people are in the same boat as you are and that I was. It seems the
two hottest subjects in support places right now are video and wifi
for people who installed 8.04. The first advice that was given to me
for my Nvidia problem was to bypass the hardware drivers manager and
go straight to Nvidia and download their Linux driver. I ended up
with a .run file that I had no idea what to do with. So I went back
to #Ubuntu on irc and it was recommended instead that I use envy.
So I went into synaptic package manager and found envyNG and
downloaded it. It required reboot. After rebooting and before the
splash screen, if I remember correctly, it brought up a screen asking
which monitor and video card I used, and which resolution I wanted to
use. I input the correct info and continued with the reboot. I got
into Ubuntu and found that I still only had a max 800 X 600 out of a
possible 2560 X 1600 which is what the card is capable of. Well last
night I received two updates. One of which, except for my login
screen being a bit messed up, fixed my Nvidia problem. So now I have
to see if the same update will help my wifi on my laptop which was
also knocked out by 8.04. If all else fails perhaps the hardware info
update that fixed mine will fix yours.