You can get good supercharger kits for the zetec from the states. I know someone who has one fitted to his mondeo. not sure what power he got out of it in the end.

on a stock 2.0 zetec, you can expect about 170-180 bhp with just throttle bodies, or 170 ish with carbs. up to 200 with cams as well. then it can start to get a bit expensive. loads of people have turbocharged them to good effect too.