Traitor
Well you'd be best finding a v. 1.5 PSP, I'm not sure what the current status is with downgraders, last I heard some FW versions couldnt be downgraded so if you've got a friend selling one or something that'd probably be best.
Once you've got your hands on a v1.5, you'll want to flash it with Dark_Alex's latest 'Open Edition' firmware, which is basically the features of the latest firmware, but still letting you run homebrew/backups etc.
For playing actual backups, its all done of a Memory Stick. So get one as big as you can (ideally a 4GB but nothing less than a 1GB), the bigger the stick the more games you can fit in, google should get you all the programs you need to get it working.
Also they have that popstation thing which I believe is a reverse engineered version of the engine that Sony 're-released' some playstation games on, and is probably worth more than most of the PSP games put together. In essence it allows you to play your old PSX games on your PSP, defo worth getting.
Do a bit of research, don't think it'll be too hard to find the stuff your after. Google is your friend!