i managed to accidently downgrade mine to 1.00 from 2.00 (no joke either).

i bought a 1.50 psp back in April (about a week after they came out) and had it for quite a while until about a month and a half ago when some of the new games started to require 2.00 to play them. well, i wanted GTA and a couple of others that required it, so i updated to 2.00 after finding out that a working 2.00 to 1.50 downgrader had been released. i just prayed it worked.

good news is, it did. after updating and playing GTA on 2.00, i downgraded it back to 1.50 pretty easily. if you need to know where i got the downgrader, send me a PM or do some searching. once you have the necessary files and all on your psp's memory stick, follow their instructions on how to downgrade. the first part of the downgrade tells you to turn on your psp and scroll to your "photos" section. open it and with the file you put into that folder (as explained in the downgrader instructions), it should turn your screen black with some white numbers on it. wait 30 seconds and then turn off your psp. when you turn it back on, go to your system settings and check it--it SHOULD say that you have a 1.00 psp (at least, that's what happened with mine--BEFORE i went over to the memory stick to click on my 1.50 update).

not sure why you'd want to downgrade to 1.00, but that should get you there. i didn't create it or have anything to do with it, but i'm just helping with the little info that i did have about that. hope it works for you (and it shouldn't hurt your psp at all--mine still runs great). good luck! and as you stated in the post at the very top, i had a 1.50 psp NEW, so i don't know what would happen if you downgrade from a new 2.00---since i updated 1.50 to 2.00, then downgraded to 1.00, then i could upgrade back to 1.50. (if any of that makes sense) haha