Yes, I know, put the disc into your computer, upload the files from there. That's all well and good, but I do not own a copy of the disc (well I did, once upon a time, but that's another story).
What kind of file do you need (yes, illegal is bad, I know) to get it onto your PSP, and how would you go about doing that? Simple terms, please, I've been researching all night, and my brain is nearly toast.
Thanks!

If you do not own a copy of the game disc, then you cannot upload it to your PSP (which only works with custom firmware anyway). .... (but like every body has custom firmware )

If you know how to make an iso image of any game (sometimes a bin file, other times an nrg file, whatever). Using the popsloader program, you'd turn that iso (or whatever format) image into a psp format file. Then you dump that file into a folder, titled whatever (IE: Legend of Mana), and toss it in the appropriate custom firmware file directory on the psp. Then like... play it from the game menu, and stuff. ;P

But please dont axe where to download the game from. Neo backhands all who ask for illegal warez and such. If you need help using the psp backup utility program, then you can ask in the general psp forum.