The timing belt is the critical link between key engine components — the crankshaft and the camshaft. Basically, the timing belt ensures that the valves and pistons/crank operate in time, and in the correct sequence. This is NOT a timing CHAIN, which is a similar but different beast. They ARE a wear item, prone to stretching, fraying and occasionally total failure – especially if you run them much past the recommended mileage limits. And if they do fail, valves hit pistons and it gets uglier than Sunday dinner at Chris Brown’s place. So heed the guidelines in your owner’s manual.
My recommendation – have a specialist do it, not the corner garage. Look on the Interwebz and in your local weekly newspaper (that one that has all of the medical marijuana ads) for timing belt replacement, You’ll probably find some deals, and if you go with a guy or girl who has done your same car a million times, it is less likely that they’ll screw it up. Savings achieved. ~ Bill