Unlock the game's cheats by buying them literally from Heidi Shadows, a Sim who sells cheats. She may appear in the following spots:

South and west of Imperial Estates between 2300 and 0000.
North corner of Park Maze between 0300 and 0400.

A slight glitch may allow you to buy a helluva lot more cheats in one fell swoop in the Imperial Gardens location; you buy all the available cheats, scroll the vendor just before she vanishes, wait until 0100 then re-approach the vendor and her wares should be refreshed.