Taskbar Live Preview not working

I am pretty new to Windows 7. I installed the upgrade (Home Premium) on my Vista desktop last night and it went pretty well. I noticed, however, that when I hover my mouse over open programs in the Taskbar it's not showing a preview of the window. Instead it's showing a box with a small icon and the name of the program:

I'm pretty sure that right after the upgrade it was showing the preview but I'm not sure what changed.
Does anyone have any suggestions?
Any help would be greatly appreciated.

Look into aero support... does your desktop show if you only hover over the mimimize desktop icon?

If not... try this.. it staightened it out for me once when it got disabled:

Click "Start" and type and enter "ap" to enter the appearance menu.
Click "best performance" then go back to "Let Windows choose.."

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