If you don't want the hassle of remapping the ECU, you could get a plug in tunit box which just plugs into the injector loom and only effects the fueling. This method gives you a reasonable amount of performance increase, but in general, not as good as a full blown remap which changes the turbo pressure aswell as the fuelling. I have run one of these for the past 12 months and 20K miles on my Passat 1.9 Tdi PD with no problems, apart from going into limp mode once, which was cured by switching the engine off and back on. Drawback is lotta exhaust smoke when giving it some.