Okay, here's a brief summary...IM me for more details.
The G60 has a 1.8L supercharged motor. It has 158hp stock at the crank. A stock charger in good shape will push about 11-12 psi. The chargers should be rebuilt every 60-70k miles. Make sure the cog belt for the charger is in good shape because if that breaks, so does your charger. I highly recommend Kompressor Kanada(
www.kompressorkanada.ca) for charger rebuilds and upgrades. I could give you many good sites for parts, oem and aftermarket. I personally like to stick to the original G60 but you can keep the charger and do a 16V swap. Other common swaps are doing a twin screw charger, 16V twin screw charger, turbo, 16V turbo. Both 1.8T and VR swaps have been do. Honestly though, if you want a VR, buy an SLC(which is already a VR).