When I had my '98 VW Passat, I was curious about ECU "chipping" the engine, after reading numerous post to the passat newsgroup. Apparently it added a bit more HP, but my delema was that the vehicle was under warrenty, and that if anything went wrong......
From what I understand, "chipping" the engine got the engine up to european specs. Those specs and special emisions consideration were not real legal here in the US.
I think there is a company called Neuspeed that makes or sells these things. The cost to do the upgrade is around $500.00 and adds 10+ HP.
Sometimes I wish I were living in the stone age. Then I would know I'm the smartest person in the world.