Wanting to become familiar with Unity before the release of Ubuntu 12.04LTS
and wanting to go from a VGA to VGA, DVI and HTMI I purchased a
PNY VCGGT5201XPB GeForce GT 520
from NewEgg. Ubuntu 11.10 works great with it.

I tried 11.04 after it came out last spring but it was slow and the
interface, I just felt I was going backwards.

There could be several problems
The download could have been bad.
Your graphic interface is not compatible with 11.04
11.10 may have corrections that might correct the problems you are having.

The next thing I would try is 11.10 and see if that corrects the problem.
If that doesn't work you might consider getting a new display adapter, that

The GeForce GT 240 is DirectX 10.1 compatible
The GeForce GT 520 is DirectX 11 compatible

If start looking for a display adapter, before you buy ask here if anyone
is using it and how well it works.

When I installed Ubuntu 11.10 the display came up in 2D. Going to the
,
it showed my display adapter with a '(version current) [recommended]'
'active'
and a '(post-release updates) (version current-update)' 'not active'
replacement
I installed the update and now I'm in 3D.
The graphics looked great in 2D and even greater in 3D.