well wat firmware do you have first of all
if you have 1.00 u just need one folder and u should put it here :a
Psp -->Game-->EX. "Doom>Eboot.PBP
if you have 1.50 you need both folders:
Psp-->Game-->EX. "Doom and Doom%"
if you have 1.5 and your'e hidding the "Corrupt Data" the files are displayed like this:
Psp-->Game--> EX> "BOR 1 and Doom_~1%" when you remane folders like that it hides the "Corrupt Data" files when you browse the games but sometimes it don't work and it gives you that message the best thing you can probably is delete the files out of there and then recopy them and if that doesn't work then you can just rename the folders doom and doom% (but there will be a corrupt file when you browse throught the games).
if you have 2.00 you need fanjita's eboot loader which can be found at
http://www.fanjita.org/psp.html :
you put the games in the same spot
Psp-->Game-->" right here " it doesn't matter what type of folder you put 1.5 or 1.00 (but is prefered 1.00) then you follow the direction from the eboot loader