I have a Pandora battery so I always use that. Having one on hand is probably a pretty good idea if you're going to be hacking PSP's, because if you brick your PSP you're going to end up needing one anyway.
That being said, you should be able to get there by upgrading to OFW 5.03. Find the updater on-line and run it from you MS. Don't update the PSP via WiFi or it will update to 6.XX and you need to be on 5.03.
Get a hold of ChickHEN and use it to run Hellcat's recovery flasher. Use that to flash M33 or Gen, or better yet use a utility like PSP Tools to Pandora your battery and use that for the flash (you can always switch it back). If you choose to Pandora your battery, and you don't have a MS reader on your computer then you'll want to make your MMS stick before you Pandora the battery as a PSP w/ a Pandora battery in it won't boot w/o a MMS stick in it as well.
I'm not going to write a tutorial as there have been plenty of them written elsewhere by people better at it then I.