Change the headgasket on 1.6 8v Astra ('98) with alloy block?

I need some tips / advice on doing the above job. I've never changed a head gasket before but I am reasonablly competent with the spanners. I've been told that I will also need to fit a new cam belt. I'm not sure how to lock the cam or tension the new belt once fitted. Any help would / advice would be much appreciated.