For Windows Users

This a bit theoretical (untested, please correct me if I am wrong)

If you don't have jruby-1.7.9 installed you can read about the windows installer here, which ideally you should install. Otherwise you will need to have a regular ruby installed (at least version 1.9.3). In any event you will need to have java installed (preferably jdk1.7.0_045), you cannot rely on the version included with processing. In addition to setting the processing root it may also be necessary to set the path to ruby-processing root in the .rp5rc file. The post installer uses wget to download jruby-complete, however if you haven't got wget, you can manually download jruby-complete and put in the the vendors folder and re-run install_jruby_complete