Learning how to drive fast on a racetrack has a very simple path of entry. Hook up with a local NASA, SSCA, or other high performance driver education group. You can find them on Motorsportreg.com or
TrackSchedule.com - Coco's Drivers Ed Calendar for 2010. No real need to upgrade the car initially, as it will speak to you when it needs something.
With enough training, practice, and seat-time, you can extract 99% out of a given machine.
Good instruction is critical, just like entering any new hobby or sport.