ok so u gotta open the pixelmon installer
then u gotta take the database file and put it in the .minecraft
then open ur mods folder and in the pixelmon installer folder u should see mods open the mods folder in pixelmon installer and there should be pixelmon 2.3.1
after u find it go in ur .minecraft and go in ur mods folder
drag the pixelmon 2.3.1 that was in the pixelmon installer into the mods folder
as soon as I try to pick a starter it crashes. i have the best forge (version 889, and according to posts above you need 799 or something in the late 700s) available to me and I installed it correctly.
What you do is download forge for 1.6.2 and set it up. Then download pixlemon. When it's done you should have a file called pixlemon 2.3.1. Whats you have that file open it with jzip or winrar or some equivalent, you should find 2 folders database and mods. In your .minecraft folder make sure to put the mods folder somewhere else. Select both thr database and mods folder from pixlmon installer and drag them into the .mincreft folder. Then startup minecraft make a new world an enjoy!