This behavior has irritated me for a long time! Andy, I tried your Ctrl-Alt-Tab trick, and it didn't work (did the same as Alt-Tab does), but then I tried another Win7 machine, and it DID work... weird.
There is another trick (easier to do than it is to describe)... Hold the left Alt key down (don't release it), then press and release the right Alt key once. Now, with the left Alt key still pressed, hit Tab and you get the old-style Alt-Tab screen.
The only other way I know to make the problem go away is to disable Aero Peek completely by doing the following:
Control Panel, System, Advanced System Settings
(or right-click My Computer, Properties, Advanced System Settings)
In the Performance section, click Settings. On the Visual Effects tab, select "Custom", then un-check "Enable Aero Peek".
There is also an Aero Peek checkbox under "Taskbar and Start Menu Properties", but this only removes Aero Peek with you put the mouse in the lower-right corner ("Show Desktop"). It does not turn off Aero Peek in Alt-Tabs.