Works for PS2 and XBOX versions of the game.
What you need: 2 controllers, 2 memory cards
What you do:
1. Start a second sim on memory card 2 ( assuming you already have a game on memory card 1.)
2. When you get to Mom's place, enter the buy menu and sell everything. Next enter the build menu and sell the walls and the plants too.
3. Save and quit.
4. Load your "main" game from memory card 1
5. Press start on the second controler to have your second sim join your main sim in the current game.
6. A chest should appear on the kerb which has all the second sim's money in it.
7. Have the second sim withdraw all of the cash from the chest.
8. Press start on the second controler and quit ( this only quits the second sim.. not the main one. )
9. Your main sim should now be around 38,000 richer.
10. Repeat until you think you have enough cash.