I've followed the instructions on this site for downloading and installing minecraft forge version 1.7.9 but when Java tries to install the files I get an error that I "need to run version 1.7.2 manually at least once." What does this mean, I've opened and played the game several times.
When installing forge you need to run the version that you are modding first and THEN install forge. So if I am going to mod 1.7.2 I would first run it normally and THEN install forge.
Run 1.7.2 at least once before you install it.