Re: Weight Reduction (JKR)
If you really want a light car for racing, I'd suggest getting an A2 or A1 and getting either a 1.8T or a built 16V in it. The MK4's are pretty portly, but then again, try and see how many REALLY light cars have good crash ratings and a beautiful interior. Unless you have a car with very exotic materials is it, it's not possible.
If you are doing drag racing here's a few tips. Over inflate the rear tires, less friction is better for tires that aren't really doing anything. Like Distinct said, don't use a full tank of gas. If you can, remove the windshield washer fluid from the tank (sounds dumb, but every little bit helps)
That's strictly for racing though. Don't try over inflated tires on the street, they'll wear out fast. Same for the WW fluid, self explanitory.