I didnt tried with 2.5 because I dont have 2.50 Firmware PSP. But you should give a try, it might work, as far as you have GTA EU.

Btw: You can use an hex file editor and edit "tetris.bin" to find/change the "MS0:/PSP/SAVEDATA/EUxxxxxxx/gfx.bmp" file path to work with GTA US or GTA DE version savedata folder, sorry for this inconvenience as it's a stupid fault on the code, cos it should read the bmp file from current savedata working directory. I'll fix it later. (not in my dev machine atm)