Go to Start/Run and type in:

regsvr32 shimgvw.dll or regsvr32 /i  shimgvw.dll

Added info:

Manually Edit: Right Click On image file. Choose Open With, then Choose Program. Select your favorite image viewer program. Check the “always use selected program” box Click OK.

To get a new copy:

EXPAND X:\i386\shimgvw.dl_ C:\Windows\system32\shimgvw.dll

http://www.tomshardware.com/forum/22592-45-restore-file-association-settings-default-icons