Ok it seems everyone isnt giving u a clear enough message...
1ST 1.5 best way to go...
if you buy 1.52 you willhave to upgrade and downgrade with the risk of bricking your psp.
2.5 is no point... its useless... u can use gta to run homebrew BUT homebrew only! no any iso's which are money savers... and dont ask how to obtain them since its illegal.
Once you have 1.5 i suggest you go to
www.psp-hacks.com and download sum nice programs 4 the psp... E.G umd emulator, fastloader, devhook ... those are the main iso loaders.
You may also enjoy other cool stuff like universal remote control.
IR shell which allows u 2 play ur own music while playing ur games.
And there are many more things available...
To sum it all up ... 1.5 has the most compatibility with homebrew...
Dont worry about most UMD locked games since there are several hacks to get around most of the games and we will probably see more games hacked.
E.G if u wnt to play gta use the MPH loader.
If u want features of a 2.5 u can use MPH fireware loader.
Mostly of all be careful when you get programs... i trust
www.psp-hacks.com
But not all files are always safe so make sure u reaserarch b 4 u put it on ur psp.