Help with 3:71 Downgrade for GPS

I need some guide: help on how to downgrade my PSP FW 3.71 so that I can use the Sony PSP-290 GPS.
I found this link in here but some files can't be download for what ever reason.
LINK:http://www.dcemu.co.uk/vbulletin/showthread.php?t=60230

I have see a video on youtube on how to mod a Sony PSP battery to a Pandora battery by cracking open the battery and d-soldering pin #4 on this chip S93C56.

and then.
Did you modify it?

If you have it, now you just need a memory stick pro duo, any one from 256Mb up to 4Gb should work.

I have a GUI to install the files you need on the memory stick, but is in spanish
http://www.mediafire.com/?2nlcnnmxx45

edit: my bad, it is in english, so enjoy

I finally got it to work,now it is 3.71 M33-2.
Thanks Mike,I speak both languages so there is no problema.

LOL
nice