evildictaitor said:
Just go to regedit and look under HKEY_CLASSES_ROOT and remove the key with the extention you want removed.
Thought I'd post the following since I just went through a few heartattacks ... all exe files suddenly became associated with Notepad; couldn't restore (because it would call up notepad; couldn't call up my reg editor (because it would call up notepad); and when I downloaded any fixes ... all but one did the same.  The one that worked came from Winhelponline in the form of

exefix_vista.reg

Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\.EXE]
@="exefile"
"Content Type"="application/x-msdownload"

[HKEY_CLASSES_ROOT\.EXE\PersistentHandler]
@="{098f2470-bae0-11cd-b579-08002b30bfeb}"

[HKEY_CLASSES_ROOT\exefile]
@="Application"
"EditFlags"=hex:38,07,00,00
"FriendlyTypeName"=hex(2):40,00,25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,\
  00,6f,00,6f,00,74,00,25,00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,\
  32,00,5c,00,73,00,68,00,65,00,6c,00,6c,00,33,00,32,00,2e,00,64,00,6c,00,6c,\
  00,2c,00,2d,00,31,00,30,00,31,00,35,00,36,00,00,00

[HKEY_CLASSES_ROOT\exefile\DefaultIcon]
@="%1"

[HKEY_CLASSES_ROOT\exefile\shell]

[HKEY_CLASSES_ROOT\exefile\shell\open]
"EditFlags"=hex:00,00,00,00

[HKEY_CLASSES_ROOT\exefile\shell\open\command]
@="\"%1\" %*"
"IsolatedCommand"="\"%1\" %*"

[HKEY_CLASSES_ROOT\exefile\shell\runas]

[HKEY_CLASSES_ROOT\exefile\shell\runas\command]
@="\"%1\" %*"
"IsolatedCommand"="\"%1\" %*"

[HKEY_CLASSES_ROOT\exefile\shellex]

[HKEY_CLASSES_ROOT\exefile\shellex\DropHandler]
@="{86C86720-42A0-1069-A2E8-08002B30309D}"

[-HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.exe\UserChoice]


The only problem I now have is re-associating the proper icons to my exe files; currently they all have Notepad icons.  Smiley