If you want to play Ridge Racer with other PSP players around you but you only have one copy of Ridge Racer, here's how you can do it:

1.Load up Ridge Racer on PSP number 1.
2.Create a game on Ad Hoc mode and wait in the lobby.
3.Take out the disk and put the game in another PSP, load the game and join the already created game.
4.Then start the game.
5.The PSP screens should now go into a black screen, after 2 or 3 seconds when the PSP stops reading the disk, take it out and put it back in the other PSP.
6.Now it should start to load up the game and after his loading is done and the track is loaded, take out the disk and put it into the other PSP and just wait till it's done loading.

Now you both will be able to play the game in multiplayer mode. This trick can work for more than two players and as the music in the game is read off the disk, only the player with the game inside their PSP will get the music playing in the background.