You are best speaking to Eshrules or Ross-Tech. I think you will need the 804 (I think) version, or maybe you could get away with the 409 if you're car isn't CAN BUS. This software is called VAG-COM you could purchase a cable from Eshrules or Ross Tech but the shareware software is free. If you want the fully registered stuff it costs $99.

I hate slow cars. I had a C200 Merc estate that was pants.

As mentioned, without a turbo there isn't much you can do with your car in terms of dramatically improving performance. You could start with a K&N air filter, but these can cause problems with the MAF.

Paul