First-Person View:
Hold L1+R1+L2+R2 on the main menu to unlock the cheat menu. Enter "FISH EYE" as a cheat to unlock the first-person view mode. Pressing Circle will change between the two views.

Cheat Mode:
To activate Cheat Mode, press L1+L2+R1+R2 at the main menu. The following cheats will be available to you:

Freeall: All items are free.
Midas: Unlock all objects, skins and two-player games.
Party M: Unlock Party Motel.
Sims: Unlock Play the Sims.

Decorating:
Holding L1 or L2 and pressing X will speed up the process of laying wallpaper or tiles