You cannot have both a supercharger and a turbocharger on the same engine. It would be practically very difficult and in any case be pointless.
Both devices achieve the same effect. They force air under pressure into the engine enabling it to burn more fuel (and so produce more power) than normal �atmospheric� arrangements. Superchargers are rarer these days. They are driven off the engine by a belt (and so consume some of the extra power produced). Turbochargers are driven from the engine�s exhaust and are more efficient.
A turbocharger has the effect (roughly) of doubling the engine�s power output. A supercharger a bit less. When Formula One cars were allowed turbochargers the engine capacity they were allowed was half that of normal cars. The 1.5 litre turbocharged cars produced close on 1,000 bhp.
I don�t know what the normal output of a 1.2 Corsa is, but I doubt it is 150 bhp, so your friend may be exaggerating slightly.
You can have both supercharger and turbo on an engine and many 'petrolheads' have done so as they give their improvements at different points in the rev range, superchargers give better improvements at lower revs whilst turbos are more efficient higher up. In fact VW now make a production Golf with a 1.4 twincharged engine which generates 168bhp and 240nm of torque.
As Norman says whatever he did to a 1.2 Corsa it isn't going to generate 280bhp and without better fuelling maps than the standard it would probably melt the head owing to under fuelling.
i may be wrong, but isn't the VW a twin turbo ? ie: one small vane which will 'spin up' very quickly and one larger vane which will produce power higher up the rev range as it has larger displacment, but isn't as 'instant' as the smaller vane, hence they have two ??
Aplogies if i'm wrong in this instance ....
And as for the Corsa yarn ........ need i say more !
.... and as far as i'm aware, you wouldn't use a Supercharger ( belt driven ) in conjunction with a Turbocharger as the practicalities would outway any (non) benefit .
Huskey, as per previous you can do it and VW have http://www.volkswagen.co.uk/new_cars/technolog y_glossary/TSI I have also seen it done on a MK1 MR2. I don't know about the VW setup but Roots type superchargers can have electro-magnetic clutches like AC compressors and can be programmed to cut in/out a pre-determined rev ranges so not clashing with the turbo's output.