- Click Start
- Control Panel
- Programs
- Default Programs
- Associate a file type or protocol with a program
- Find the extension you want to change (.doc), and select it
- Click Change Program
- Select the program you want to use from the list. If it does not appear in the list, click browse and find it. It should be somewhere under Program Files ("Program File (x86)" if you're using Vista x64). On my system WINWORD.EXE is in "C:\Program Files (x86)\Microsoft Office\Office12"
I really can't get any clearer than that!