its actually a pain in the ass to Downgrade from 2.00 to 1.50
The easiest way is to either have Lumines (Unpatched/non greatest hits) and upgrade to 3.50, then downgrade from there. Or to have a Pandora battery, which can be made by either having another PSP that has CFW, or you can Solder the battery, or get it from ebay.
I will PM you the link of where i get the files to downgrade/upgrade to CFW.