I know this works for real, as I have seen it happen!
Note: It may not work first time.
99,999 Bells in 14 easy steps:
Step 1: Go to the Town Hall.
Step 2: Go over to the post office area.
Step 3: Talk to Pelly and select 'Acess Account'.
Step 4: Select 'Save Bells'.
Step 5: Put an amount of Bells in.
Step 6: Save your game and turn off the DS.
Step 7: Take out the Game Card, unless you have the Manual Startup option enabled, in which skip to step 8.
Step 8: Turn on the DS.
Step 9: Go into options and change the year to 2099.
Step 10: Turn off the DS again and put in the Game Card, unless you have the Manual setting on, in which skip to step 11.
Step 11: Turn on the DS (Tap the game on the menu if you have Manual setting on) and wait for the title screen for Animal Crossing: Wild World to load up.
Step 12: Tap 'Continue'. Select the character you had the savings on.
Step 13: Look in your mailbox. You may have a letter from the Town Hall.
Step 14: Go and get your lovely dosh at the Town Hall!
Splash your cash however you want, or try again.