In Vista, how does one establish a Rexx program (ext: .rexx) as the default program for a particular filetype?
Specifics: the particular filetype is .ppw and the program to process them should be PPWIZARD.rexx
Associating File Extensions with Programs in Windows Vista
If you have Windows Vista, you're SOL. No, seriously, Vista does not come with a utility to modify file associations the way you can in Windows XP. The only way to do this is to edit the registry directly, or purchase a 3rd party program, such as Creative Element Power Tools (see File Type Doctor, $18), or some similar 3rd party Windows Explorer replacement program such as Directory Opus 9 ($75).
Directory Opus: http://www.gpsoft.com.au/
Or you can try the limited functionality Vista does offer: