Are you trying to brick your PSP? lol. I didnt even know you could put programs on the PSP like these.
I know it's definitely possible (you can install windows 95 on your psp if you really want xD) As to which program I have little idea.
If you have a linux/unix emu running on your PSP you can use Pidgin. Source code available here: http://www.pidgin.im/download/source/
Just go to ebuddy.com with you psp and log in to the service you want. They have msn, aim, yahoo, and google talk.