When you right-click a file, you see the menu option “Open With”, which provides a list of programs for you to open the file with. You can clean up the Open With list by using a Registry hack. Run the Registry Editor (Start Run Regedit) and go to the key:
Look for the file extension whose Open With list you want to edit and find its OpenWithList subkey. The subkey will have an alphabetical list of String values.
Open each value and examine the value data. It will be the name of one of the programs on the Open With list .
Delete any entry you don't want to appear. Don't delete the value data; delete the String value listing. In other words, if the value data for the String value is Winword.exe, delete the entire string rather than just the value data. Exit the Registry.
"Windows XP Tips: Clean Up the “Open With” Menu"
Reference : techpraveen.com