My impression is rather you have inherit a someone else's project, and you must repair it, which is a hard thing to do even for experienced coders.
OK, I've seen some errors again:
Remove always the last identifier (the last comma) at the end of the elements of an array or an object. At least till IE7 and IE8 are in use.
You miss the final parenthesis: should be MM_preloadImages(...). And use the comma as delimiter between all those arguments.
It's a little bit crappy, that document...