I know this is a rather old topic, but I also never liked the Areo Peek feature when using Alt+TAB to switch tasks. Furthermore, I don't refuse Areo Peek completely - for example, I like just having a look at my Windows desktop using WIN+Space.
I tried a lot to disable Areo Peek just only for Alt+TAB task switching, but nothing really worked for me. I know about all the registry hints, for example setting the Aero Peek delay in milliseconds to a very high value. But this does not work, at least not on all machines - from my experience, you can set a high value which is still limited to 3000 ms internally (maybe this worked before the Service Pack for Windows 7).
So I decided to go another way and try to solve this issue via AutoHotkey. This script disables Aero Peek just for Alt+TAB, and only for this - so you can still use the other Aero Peek features.
The script is tested against AutoHotkey Version "AutoHotkey_L 1.1.00.00" with Windows 7 Professional 64 bit with a Windows user with admin rights - and until now reported to work on all systems I got feedback from. Just install AutoHotkey and set the script file to be run automatically when Windows starts. It is very lightweight, using only very few resources and CPU time.
I just post it here in hope this will help anyone having this issue. Please download the script from:
http://dl.dropbox.com/u/15020526/Privat/Software/GA/AutoHotkey/DisableAeroPeekForAltTab_1.0.zip
You can distribute it freely, under the FreeBSD-license.