I usually do not have preview pane activated in Windows Explorer, so I did not notice the Acrobat preview under Windows 7 64bit is broken. Further investigation shows that not only the preview doesn’t work, the thumbnails do not work either. The issue is actually over 2 years old. It happened ever since Microsoft introduced 64bit OS.
pretentiousname.com has documented the problems extensively, they also offer free solutions. It’s surprising that neither Microsoft or Adobe cares to offer patches to fix the problems. The preview problem is only a simple registry fix. The thumbnails problem is harder, you need a software “bridge” to get the thumbnails to work. You can find out the registry fix and the software bridge from the site.