The quickest and cheapest thing might be to take the current bike to a bike shop and ask them to replace the cassette and chain. You can also replace the tires with slicker ones that are a little faster if you feel the bike is too slow, and keep them pumped up to the max recommended pressure. That'll speed you up a lot but you can still hop curbs with impunity.
They may also tell you your hubs or bottom bracket are shot...when I've bought old bikes those are often the parts that need to be replaced first.
Last edited by cooker; 10-20-07 at 06:04 PM.