The Jupiter Moon Simulator Program uses the low precision routines published by Jean Meeuse in his book Astronomical Algorithms.  You can order the book from William Bell (http://www.willbell.com/math/mc1.htm)

The program does not require an installation.  Just extract the entire contents of the zipped file into the same folder and then double click on the file JUPMOON.EXE.  

If the program does not run, make certain that all of the files are in the same folder.  You will need these four files in the same folder:

JUPMOON.EXE
EYEPIECE.TXT
GRS.TXT
OBJFL.TXT

You can also put the file JUPMOON.ICO in the folder if you want an icon for the program.

You can edit the text files to replace the default paramaters with your own.  If you do make sure that you place the data in the file the same way it appears.  It's best to just type over the existing data rather than start from srcratch.

The program defaults are for a common eyepiece list and a 80 inch focal length objective.

The Longitude of the Great Red Spot (GRS) is contained in the file GRS.TXT.  The current value is 77 degrees.  The program uses this value to calculated the parameter GRS Delta.  When the value of GRS Delta is zero, the GRS will be at the center of the planet.  The GRS moves from time to time, so you will need to update this number occasionally.  You can check the accuracy of the program and obtain the latest value of the GRS Longitude fro the Sky and Telescope Website (http://skyandtelescope.com/observing/objects/planets/article_107_1.asp).