Firstly, you should not start any post with "Urgent" or "Really Urgent". We all are doing this on our own time and noone else's problem is "urgent" to us. Often, long time posters will simply ignore posts with a title like yours.
That aside, have you tried typing in jbuilder to a console? Normally the program's name is also it's executable. Have you looked in the "Start Menu"?
Shortcuts do not always turn up on the desktop automatically, often we have to manually put them there.
You could always try issuing a whereis jbuilder. It will tell you where the program is installed. If all else fails, the readme file should tell you where the executable resides.