Well this is illegal. If you still want to do it, I will explain it, but not tell you how.
NOTE: I am not responsible if your psp gets bricked.
First you have to get custom firmware on your PSP (which version is it? 2000 works, but I don't know about 3000). To do this, you will have to get a magic memory stick (where the software to flash it will be loaded on to, search on google), and a pandora battery (which will allow it to flash, search on google). Magic memory stick + Pandora battery = Custom firmware
Then you will have to download the PSP game ISO little big planet which is illegal, search on google. Goodluck.