Show File Extensions.

Windows XP
Click 'Start' then 'My Computer'
Click 'Tools' then 'Folder Options
Click on 'View' in the Folder Options window
Unmark/Mark 'Hide extensions for known file types'
Click 'Apply' then 'OK'

file extensions XP 		Windows Vista
Open any folder, or open explorer
Click 'Layout' (to the left of 'Views')
Click 'Folder Options' then 'View'
Unmark/Mark 'Hide extensions for known file types'
Click 'OK'

Click 'Apply' then 'OK'

file extensions Vista
Wyrdjax
Jack Frost & The Hooded Crow