I had the same problem, and according to my googling, so have many, many others. Dell tech support was sure that installing new drivers would fix it (it didn't), others have suggested
switching the resolution of your wallpaper image to match the screen's native resolution. That doesn't work either. Nor does switching to a blank screensaver (another web suggestion).
The actual culprit is TMM, Vista's process that looks for multiple monitors and attempts to intelligently modify resolution. If you aren't using multiple monitors, you can disable TMM:
1. right-click on 'computer' and select 'manage'
2. on the left pane, expand 'task scheduler' then ' task scheduler library' then 'Microsoft' then 'Windows' then 'MobilePC'
3. select TMM in the center pane, then on the right pane, choose 'disable'
Now you should be able to close your laptop, let it go to sleep and when it wakes up it will still be in your preferred resolution (also, the screen won't go blank for a second right after waking up)
I'm not sure if you will have to also disable it for future windows sessions (maybe in the 'triggers' tab on the bottom of the center pane).
