Changing auxillary belt on 3.9 V8 ES Auto

I'm thinking of changing the aux belt on my Discovery 1 1995 3.9 V8 ES Auto. Is there anything to watch out for? Does anyone know if it has a pre tensioner built in? Would I be better off letting the garage change it for me, or am I worrying about nothing?

Ta

Ray

Nobody replied so I had a go at changing it myself! Three words sum it up best, "what a pig". I guess the LR garage must use some sort of special tool to move the pre-tensioner pully into the correct position so that the belt goes on. I just used a two foot long bit of metal conduit pipe and a lot of brute force but got the bugger on in the end! All in all still worth doing it myself but without the correct tool really needs two people.