It often feels like the second we walk out of the store with a new PC, it's instantly out of date; there's always a new chipset, new OS, new graphics card that outshines our home computer. But, just because your old machine doesn't have the goods to run Vista, doesn't mean it can't still do you a ton of good. Try these wallet-friendly tricks to put your old desktop to work. Here are 15 great uses for an older PC that prove it's worth keeping around.