Whats involved doing it, and is it a big job??

 

You need to take the cambelt off really although it can be done without taking it off but it's a bit fiddly. Great little "how to" here:

http://www.projectpuma.com/viewtopic.php?p=53096#p53096

You can see it here bottom right with orange sealant on it and right behind the cambelt:

 

sweet mate nice one !!

 

and if your taking the cambelt off you might as well replace it and the tensioner at the same time!