Alright, let's try something more complex. We're gonna manually add java to your system path.
First: note where on your computer your JRE is located.
Second: go to control panel -> system & security -> system -> advanced system settings
click on "environment variable", find the system variable called "Path", then hit "modify"
Now be careful, you don't want to erase stuff that is in the "variable value" field, instead go to the end of that field (click it, then hit the "end" key on your keyboard), add a ";" then the path to your Java Runtime Environment, (for instance, mine is "H:\Program Files (x86)\Java\jre7\bin")
Click on OK to close the various windows, open up a command line prompt, enter "java -version" to verify that it is properly installed, this should display something that looks like this:
java version "1.7.0_45"Then navigate to wherever FreeSpaceOpenInstaller.jar is located then try "java -jar FreeSpaceOpenInstaller.jar" again.
Java(TM) SE Runtime Environment (build 1.7.0_45-b18)
Java HotSpot(TM) 64-Bit Server VM (build 24.45-b08, mixed mode)