In windows, we open some files with other supported applications too.. like mp3 files we can open with winamp, media player, itune, or many other mp3 players...
Now here ill tell you hack for how to remove unwanted applications from this open with list..
This is very simple n useful trick

lets go..

Settings:-

1] Run > regedit > hit Enter
2] Registry > My Computer > HKEY_CLASSES_ROOT > Applications
3] When you expand 'Applications' key then you will see a long sub keys list of program names
like accwiz.exe, BitTorrent.exe, n something like more list..
4] Then select a application key which you want to remove from 'Open with' list..
(e.g.- i selected 'flash.exe' to remove from list)
5] Right click in right side pane in blank area or go to Edit> New
6] add New> 'String Value' (REG_SZ)
7] Change name of string value as 'NoOpenWith' (case-sensitive)
8] We Don't need to set any value data for this string..
9] Refresh your desktop n check open with list for any file..

Finish... :-)