A broken timing belt means bent valves or worse.
I actually saw a TDI, 1.9L Diesel once where the belt broke, and in the process of the valves being hit, it caught one of the valve heads, bending it, sent it up at an angle, and actually knocked the mechanical injector out of the head, destroying the actual casting of the head.

Actually, I saw two where this happened, but the other one broke a motor mount, causing all the mayem, so that one doesn't count....
Like Travis said, you can put some things off, but i would not reccomend putting off replacement of the timing belt. and, for the later cars, always do any tensioners, idlers, and water pumps while you are in there. It ain't cheap, but it's a lot better than the alternative.
