I could give you s step by step guide.....but you'll have to be experienced with car audio gear installation and pulling apart certain interior parts of your car. If not its far better to head into your local car audio shop and pay them to install it, should cost around the $100-$150 mark i'd imagine, more for the cables required if you dont have them.
Chris if you have a fair idea on what your doing, then i reccomend just getting stuck into it, and if you have any problems along we way, im sure you'll get the answers on here. But like Holdenboy was saying, you'll need a bit of knowledge and experience, so if you haven't got that, then take it to a specialist.
You will need a fused distribution block, so you will have a fuse at the battery, then 2 in the distribution block. This is one area that you don't want to cheap out on coz a fuse is all thats between your dodgy wiring and your car becoming a fireball
I mounted a 4 channel amp under the seat of my vs, was a little large and fasioned a cover plate sort a of a Z shape to look at it from the side, then attached it to the floow and the amp with velcro, stopped people kicking the amp.
Another point to think about: is there any specific point to run the amp power cable through the firewall that is easy. Remember it was a pig of a job in my VS and took ages to finesse it through, and hoping someone has some ideas on how to do it in a VZ, whether there is a spefiic spot to go through