Firmwares(versions) enable your PSP to do different things. For example ver. 2.0 and up allows you to web-browse, whereas if the ver. is lower then 2.0 you can't. If a PSP has ver. 2.0 and LOWER it allows you to play homebrew(games that you can load onto your PSP) and if it is 2.1 and above(like yours) you can't. 2.5 is only a bad thing if you want to play homebrew. However, if you have GTA you will be able to play homebrew, you can find more about homebrew in the "Homebrew" section of the forum.
