PSP Slim Unlock Help

[Zinmasterb]

Alright well I've been looking around at guides for this and all they lead to is confusion.
Pretty much what I need to have clarified is:
Can I install the M33 unlock on any firmware?
If not, is there any way of unlocking old firmware outside of buying the $60 pandora battery/ mem stick combo? And why does that come with a battery anyways? I assume the mem stick contains the file that downgrades your firmware but what does the battery do? Just jack up prices?
I just realized my old bulky PSP isn't working and since I'm about to go on a trip where a good portion of my stay will be on a plane I really want to have my PSP unlocked and ready to go by then.

edit: Alright I think I can manage to debrick a PSP Slim with my friends PSP fat but it has FW 3.6, could I transfer 3.6 to the slim and then downgrade off of that, or would I have to downgrade his PSP initially?
edit2: Looks like 3.6 is the ideal FW to have your slim at, so I guess I'm pretty much set.

Alright, since I solved the last problem here's a new question...
Anyone have any simple FW they can reccomend?
I'm particularly looking for one that can manage music well and works with itunes, and one that can transfer e-books into .txt files.