Firstly, read this thread:
http://www.mk5golfgti.co.uk/forum/index.php/topic,1797.0.html - and in particular, download this:
http://vwts.ru/engine/bpy/bpy_15-1.pdf, this:
http://vwts.ru/engine/bpy/bpy_19.pdf, and this:
http://vwts.ru/suspension/g5/g5_40-7.pdf.
The actual changing of the belt, tensioner and idler rollers has got to be one of the easiest on the planet - but the prep work is an utter ba$tard. You need to: disconnect the exhaust at the turbo, disconnect both driveshafts at the transmission (OK, you can get away with leaving the left one attached), completely remove the right engine mount, jack the engine at about 45 degrees, then remove the right engine mount support - only then can you gain access to the cam belt and tensioner.
If you have a Haynes manual - IGNORE their method of setting the tensioner - it is WRONG. Use only the method described in the official factory workshop manual for setting the tensioner (pi$$ easy - not rocket science, and no special tools needed).
If you are gong to do this, with the waterpump, fully drain the coolant. The radiator has quick release hose connections top and bottom which need removing. But also remove the lower hose on the auxillary electric coolant pump. Go to your nearest Cromwell Industrial Supplies (
www.Cromwell.co.uk) and purchase a small tube of Rocol Sapphire Aqua Sil silcone grease -
http://www.cromwell.co.uk/ROC7706140Q. Apply a thin smear to the plastic flanges on the radiator (where the quick release fittings go), and also to the rubber 'O' ring and flange on the water pump.
Pre-mix your new coolant to a 40% concentrate (50% mix is too high in the UK). You will probably only need two 1.5 litre bottles of G12++ coolant. Never, EVER use a non-genuine cam belt kit.
Oh, and you do NOT need new bolts for the engine mounts - they are NOT 'stretch' bolts, so they can be re-used.