[mythtv-users] [OT] Why doesn't my desktop size change when I change resolutions?

[William]

This is a bit off topic but the system that is giving me problems is my
Mythtv system so there is the tie-in.

I am running FC1 with the latest nvidia drivers and a FX5200 graphics card.
Set up per Jarod's howto. Because I am directly driving a HDTV monitor I am
running a pair of custom modelines. They are basically 1920x1080i and
858x540p. Here is the issue. The desktop resized itself to fill the
1920x1080 screen which is fine but it did not resize again when I switched
back to 858x540. (Better picture at the lower res, go figure) So now I have
a window onto the desktop that I can scroll around by "pushing" on the
screen edges with the mouse.  I could live with that but the video from
mythtv is also still displayed at the higher resolution too.

Here is my question: Is there a way to tell FC1 to always resize the desktop
on a resolution change or is there a way to manually set/modify a config
file to match my needs?

TIA,

Bill