Pixmap corruption

Hi,
  On my Toshiba Satellite Pro 4300 laptop I get pixmap corruption.
(I think pixmap is the right word - all the icons etc)
They often disapear, and half appear etc.  If I move my mouse over them I get 
them back, but only temporarily.

For an example, I loaded up kmail, and the icons across the top are all fine.  
However the icons next to inbox,outbox, etc etc  are all gone.  If I move the 
mouse over any of them, the ones under the cursor reappear.  If I cover up 
the window, or minimise it etc, then uncover the window, the pictures are all 
gone again.

I searched the archives as best I could and haven't found anything.  Any 
ideas?

JohnFlux