OK use your favourite text editor to open ~/GNUstep/Library/Windowmaker/menu . When you scroll past the comments, you'll see the definition of your menu. There you can add the following item:
Code:
"Run program" SHEXEC %a(Run, Type the command to run: )
The clue is to use the %a() stuff instead of simply the name a program, as is the case with normal mentu items.
(It may also be possible to do this using the WPrefs or wmakerconf programs, by creating a new "Execute shell command" item and putting the %a(...) as the commmand.)
Regards,
nukkel