I have a 2004 cavalier with the 2.2L Ecotec motor. I was thinking about getting a 2.0L Supercharged Ecotec crate motor from GMPartsDirect. What would be needed and how hard would it be to complete the swap?

You would be better off finding the front clip off a wrecked Ion Redline or Cobalt SS, you need the PCM and wiring harness, and also probabally the guage cluster and maybe the gas pedal.

why go with a 2.0L supercharged when you could spend $3500 and get a turbo kit. i got a hahn racecraft stage 2 and i am killing cobalt SS's and SRT4's and that is at 9psi

The real problem is finding out if the Cavalier ecotec PCM programming is compatible with the LSJ(2.0SC). Which I'm not sure it is. As well as the BCM, and guage cluster, which controls the speed & odometer & the thieft deterent system.

parts would need:
engine harness
PCM
Transmission (saturn LSJ's have different manual trans then L61)
fuel rail harness
SC harness

parts might need (not sure about)
BCM
guage cluster
boost gauge
boost gauge harness

There might be more parts, but again not sure. Besides those parts there brand new are quite expensive. Most likely you won't find them in a junk yard, cause of how new. New parts would cost as much as a turbo, not including the engine on top that.

Jonathon is got the better idea. You could also salvage a turbo system off a Saab 9-3, sinve it's a basic ecotec with turbo.

I´m thinking of the same route. For my conversion I need a 8-hole (?) flywheel to mate the SC engine to the existing gearbox

If you want to go with the LSJ, you should buy the front clip. Then get a megasquirt to control the fuel with the LSJ PCM controling spark.