I think you set your *virtual* desktop to a res of 1024x768. That means you can scroll through it while at a lower res. So i suggest you change your real resolution to 1024x768, and if that doesn't work you probably have video card or monitor probs.
I installed Mandrake 9.1 with an radeon 9700 and everything worked fine (except for the bad 3d acceleration...

)
Dennis