Place theme.p3t file in X:/PSP/THEME/ folder and select theme from XMB->Settings->Themes
where X is your psp USB or PSP media card
Currently Playing: Jet Set Radio (DC), Triggerheart Exelica (DC), Rez (DC), GTA IV (PS3), Mario Kart (Wii), The World Ends With You (DS), Kingdom Hearts (GBA)