not large enough to display the application in red hat linux x win desktop

I use red hat linux es 5
I use startx to start the x-win desktop.
But when I use vritual manager .
The display application is too large so the bottom
part for the application cannot show out.
I cannot scroll down to get the display of bottm part .
So, I do not know what button display at the bottom part.
So, what can I do .
I already set the display to 800x640 already.
Please advice