some folks on this board have had good luck with a scan unit sold by "harbor freight" for less than $50. i have recently purchased one of Alex Peper's scan tools for use with a PC. i haven't used it much but it appears to be pretty impressive. they cost $122 at obd-2.com though they can be had open box on ebay for a bit less. the only problem i've had was the need to reset the display properties to see the whole screen.

this whole obd-2 and can thing is really beyond the scope of the average owner and i think a tool that gives you the codes and resets the cel and service lights is about all you can use. you could go full on vadis and spend 3k for the interface and the software and then you would be able to reprogram the car but that seems a lot to spend on something with a finite life and will not support new cars. i would go cheap and maybe buy from a store with a good return policy.