Would get the experts to do if I were you bertson - it's not as easy as it looks!
We bought one at an auction and fitted it ourselves - we had huge problems afterwards with the sealing and subsequently when the fire was lit, the room became smoky after a time and was no doubt full of carbon monoxide.
We've since had it replaced and fitted by a professional firm and it's working beautifully.
Another tip they gave us is to spray WD40 onto the cast iron suround - we did this at home on our 6 year-old surround and it looks like new again!