Fitting an underdrive pulley kit

[Sidzrx]

I'm planning to fit my underdrive pulley kit, I've just had a go at doing it, but I can't get the alternator pulley off of the alternator. Is there any special way of doing it?
There obviously must be a way of locking the alternator in place so that you can undo the nut on the pulley but how?
I tried holding the alternator in place with a screwdriver, but I stopped in case of damaging the alternator.
Anyone done this before who could tell me how to do it?

[memski]

Take it to a garage, airgun is the easiest way.

[Sidzrx]

I've got an airgun myself, but don't you need still need to hold everything in place?

[RobbieRX-7]

Mate, but the belt back on. Tension the belt really tight, and zip it off with the airgun. The pulley comes right off in a second. Obviously when you fit the new pulley, do the reversal or removal procedure, but loosen the belt so you have about 1/2 inch deflection between the alt pulley and crank pulley. If you leave the belt too tight, you can damage the bearings in the alternator