very easy in Win98, just go for View -> Options and you can choose which files to konfigure.
Another way is to use the Registry with regedit (Be aware, everything is done in your Reg, making a mistake can be very "awesome" for your system!)
Go to HKEY_CLASSSES_ROOT. There you�ll find all types of files with their name +"file" or "_auto_file" (not this long list with .* , scroll down!). Open the subkey "shell", if there�s no key, create! Search for the object to edit and open "command". There is your playground. If you want to make a new one, create a file in "shell" with the name of your command, create a subkey "command" and define the path to go afterwards.
For example: If you want to open your .exe files with HexEdit.
Path:
code:
HKEY_CLASSES_ROOT\exefile\shell\Open with HexEdit\command
command:
code:
"c:\hex\HexEdit.exe %1
Your printer or desktop have special subkeys you�ll find in HKEY_CLASSES_ROOT\CLSID
If you got more questions or need help or still haven�t found cense�s reply feel free to ask.