You gonna have to go the long way round.
Click on 'Start' then 'Run' and type in there:
Notepad
Click Ok and Notepad will open.
Now click on File - Open - and browse to your .cfg file

Not sure how Vista works but in Xp to make .cfg files always open in Notepad:
From Windows Explorer, at the top, click on 'Tools' then 'Folder Options' then 'File Types'
Go down the list till you find 'CFG Files', click on it, then click on 'Change'
Look down the list till you find Notepad and select it - click Ok.