ok as a person that just bought this about say 3 months ago and uses it for everything to Homebrew to running PDA-ish programs and Stepmania - and every emulator out there i can break down useful sites like this.
First you need to know what you have as far as FW that comes with the PSP - my slim came with 3.6 OFW(official Firmware) after a trip to ebay and lots of reading i came to the only way to install a custom firmware is via a trick called PANDORA BATTERY + a memory card made with an already custom firmwared PSP .. since i didnt have one around i bought a package on ebay by searching Pandora battery on ebay - be forewarned that xmas has made prices pretty high - i bought mine for about 65 bucks few months ago this is what u see now mostly
http://cgi.ebay.com/Pandora-Battery-1GB-Pro-Duo-for-SLIM-FAT-PSP_W0QQitemZ180185001321QQihZ008QQcategoryZ122516QQssPageNameZWDVWQQrdZ1QQcmdZViewItemWhat the Pandora battery does is puts the PSP into Service mode and then runs the program off the memory stick which in turns installs custom fireware into the flash - the best CFW for slim atm is the 3.71M33-3 which is what most ebay auctions come with
after you get it installed with custom firmware you have the following options.
one the best site i have found for homebrew/psp things is
http://pspupdates.qj.net/they are updated with stuff everyday and usually on the top of a lot of peoples lists when they add new stuff to homebrew.
for emulators i recommend the above and
http://www.dcemu.co.uk/mainly browse these places forums for stuff you are interested in - if u want roms well you can torrent those mostly - installation may seem confusing at first but pretty much for all homebrew it will be like this
unzip the download and place it on a memory card in these folders MS0:PSP/GAME - MS0: just stands for the memory card inserted
after you copy the emulators folder into the "GAME" folder it should show up under games in the XMB menu on psp - there is always a lil more to it then this once u add in roms and stuff but trust me its not difficult the only thing u want to read up on with the psp before jumping into it is when messing with ur PSP\'s Flash - because thats where potential bricks happen.
if you want ISO\'s or CSO\'s of games... well thats your own business i know of some sites but ill keep it off the forums. also if u want to check out some just in all good info here are two links 1 for reccomended games for psp and other for reccomended Homebrew - with homebrew it takes a lil work to get it working sometimes because psp slim does not support the 1.5FW kernal like the old Phat ones
http://www.neogaf.com/forum/showthread.php?p=6643052&posted=1#post6643052http://forums.qj.net/f-psp-homebrew-discussion-12/t-guide-top-rated-homebrew-for-15-custom-firmware-41416.htmlif you got any more questions just let me know - i have read tons on this stuff and there is tons of potential ways to use ur psp even if u want to run another OS and stuff its possible altho not that stable - also even possible to use it as a GPS if u import the japanese accessory