i just downloaded tales of the world radient mythology and put it in the ISO folder, put a UMD in, and pressed play. but it said game could not be started (80020148). any suggestions?

If it's a new game it probably needs higher than 3.03 firmware.
You might want to try installing 3.40 OE - 3.40 OE-A Easy Installer.

I downloaded this and put the two folders in to the GAME folder and went to run it on the psp and it says "The game could not be started. (8002014c)"?? Am i doing it wrong?

Sorry i have moved them to GAME150 now

And did it work?

Yea, but i dont know how to get Black Flame XMB theme because when i try to move the folder to Flash0 it says there isn't enough space. Do you know how to fix this?

free up some flash0 space... but make sure to make a backup of your flash0 first...

http://www.psp-spot.com/forums/index.php?showtopic=40933

To run isos and csos on a psp no matter what firmware you have you need a umd inserted to trick the system. i use gta liberty city storys. good luck!

Not quite true any more, custom firmwares have a "No-UMD" mode, which you can turn on through Recovery Mode.
3.52 M33, for example, has the "Sony NP9660" No-UMD driver which has over 99% compatibility (I think).