When you use the Open With context menu, Windows 2000 records the program used to open the file extension.
If you accidentally opened a file with the wrong program, you can remove the entry:
1. Use Regedt32 to navigate to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\<.extention>\OpenWithList.
2. Each entry uses a value name that is a letter, as in a, and a data string which is the program that opened the file, like Notepad.exe. Locate the program that you wish to delete and record the value name. Delete this value name.
3. Edit the MRUList value name and remove the letter that you deleted.