homebrew PSP dev Liquidzigong has released a new cfw "5.50 prometheus" for PSP-1000 & 2000 allowing you to play 6.20 fw required games without decrypting & patching any disc images. prometheus first started out as another brew for decrypting 6.20 fw required games. Liquidzigong was rumored to take 5.50 GEN-D3 and integrated it with prometheus. in either case it is newer type of cfw.
a. GEN-D3 cfw is needed first to install 5.50 prometheus. its still not certain if prometheus will be compatible with GEN-D2 but you can use the GEN-D3 to D2 switcher to test it out. this cfw cannot be installed on a PSP running on M33 cfw.
b. copy and paste 5.50 prometheus to ms:\PSP\GAME and browse for it in the xmb.
note: prometheus 5.03 cfw is also available for PSP 2000/ta088v3 and 3000 models (your PSP-3000 will need to be on 5.03 ofw for this to work for).