is it hard to do yourself ? and are there any guides on here

Which engine? I have done my 110TDi. Not the most pleasant experience in the world, but perfectly doable should you have appopiate tools. One of the hardest bits I found was removing an engine mount, which seemed to be impossible (I slipped the belt around it in the end, using the water pump hole!, and a tool for tensioning the belt tensioner pulley.

The first change was done before I bought the car, and I did the second change at a 120k, now at 135k, not sure if I'll do it again, or stump up the cash and pay a garage for the 3rd belt, shall have to see how I feel when it reaches 180k.

Some cars have a chain which never needs changing, anyone know why Octy engines don't have this?

Some cars have a chain which never needs changing, anyone know why Octy engines don't have this?

Cost.

I though that even the fabia (the older 1.4?) has a chain, but there is still a good posability it would need changing at 100k+ miles?

the 1.8t has a chain across the 2 cams and a belt 2 drive the rest.