I recently bought a 1.52 PSP and upgraded to 2.0 using the GTA UMD. Last night I attempted to downgrade in the standard method from the tutorials and it didn't work.
THen today I read a tutorial that states you should not update with a UMD. Have I inadventantly screwed myself? Can I not downgrade now?
Thanks so much!

You can still downgrade. Just follow the steps.

Thanks for responding.
I've tried numerous times:
After I've fooled the PSP into thinking it's 1.00, I go to the game menu to run the upgrade and it tells me there is a corrupt file where the upgrader to 1.5 should be.
Please help.

i think that you have put the file (EBOOT.PBP) file in the wrong spot put it in this directory in all caps to or else it won't work
(drive):/PSP-->GAME-->UPDATE, "EBOOT.PBP" (THE UPDATE FILE 1.5)

the downgrade will still work since that is how i did it along time ago upgraded with GTA then downgrade it with the MHP or MPH what ever it is...JUST follow the step carefully

its not bad you can still play homebrew on 2.0

wait, u can play homebrew on 2.0? i thought it was only for versions 1.5 and below!

You can run certain homebrew on 2.0 but not iso's. To downgrade to 1.5 you do not need to fool your psp into thinking it is 1.00. Also make sure you name all the folders right. For example, make sure your update folder is in all caps.