This is a video tutorial I made a while ago, for downgrading a PSP 1000 or non-088v3 2000 with 6.20/6.31/6.35 to 5.00 m33-6. It assumes that you have HEN installed for version 6.20, version 6.31, or version 6.35. For help installing HEN for the listed versions, click one of these links:

6.20: Watch Video (PRO B5 Tutorial)
6.31: Watch Video (6.31 PRO Tutorial)
6.35: Watch Video (6.35 PRO A3 Tutorial)
(*Note: I know these particular HENs may not be the most current, but they will work for all intents and purposes.*)

Once HEN is established, follow the Video Tutorial below.

Thanks, hopefully this helped some people.