the turbo and manifold from the saab 9-3 aero 2.0T (2003 onwards) and the vectra 2.0T will directly fit the 2.2. However there are 2 different type of turbos, a garrett (too small) and a mitsubishi.
you will then need to sort out the oil and water supply/return. Water is pretty easy, however the only way i can see of getting the oil back to the sump without drilling it is to remove the sump plug and connect the pipe to that.
crankcase oil breather is pretty easy just connect to the inlet on the turbo
a new exhaust downpipe will have to be custom made, this will need to go into a minimum 2.5" exhaust
intercooler/chargecooler is pretty easy to plumb in, space may be limited
new injectors will be needed, but the ones off the z20let will work
courtenay sport have confirmed that the ecu can be remapped
an external boost controller is a good idea
the main problem ive found is the amount of space in the engine bay, dont know about the astra but a good chuck of the boot will be lost on the vx220 as the manifold and turbo extend about 9" from the exhaust ports of the engine.
all in all, it is possible and it does take a bit of work but turbo charging is a hell of a lot more efficient than a supercharging and the turbo is not that big to cause huge ammounts of lag.
ive managed to source 2 mitsubishi turbos, an inlet manifold, all gaskets and oil/water pipes for less than £200.
i reackon for a total of £2000 i can have it turboed at about 250bhp