Invalid resolution when using CTRL/ALT/F1 - how to fix (ubuntu 8.10)

[Chris G]

I'm running xubuntu 8.10 (though I suspect the problem is common to
all 8.10 versions).

I can run X fairly reliably though I do have some issues when logging
in and out presumably due to switching resolutions.

However switching to a console using CTRL/ALT/F1 (or any of the
others) doesn't work.  I just get an error message from my monitor
saying the resolution is invalid.  My monitor is a Dell 2001FP capable
of up to 1600x1200 so I suspect that the CTRL/ALT/F1 is switching to a
totally impossible resolution.

How can I fix this problem?  Is there any way to specify the mode and
resolution to use for the text mode consoles?

-- 
Chris Green