Mapthis! is a GPS navigational software tool for the PSP. You do not need a GPS unit to use it, but do of course need homebrew. I use it and it's pretty cool.
http://www.dcemu.co.uk/vbulletin/showthread.php?t=32582
You'll have to read everything and figure out how to extract the maps from Google Maps. It also helps to have a large memory stick. I would say 1gb minimum, but 2gb gives you a little more to play with. Transferring the program itself dosen't take too long, but the map files take a VERY long time to transfer over. Don't let this deter you; it's a very good program.
I have my own maps extracted of Vancouver. There's a bit of a learning curve, but nothing you can't handle.