serpentine belt replacement

while my truck was at the dealership today they told me that my serpentine belt needs to be replaced. the truck is a 2.7L 2001 w/ 123K miles and i have never changed the belt but it has never squeaked or squeeled or given me any problems so i never bothered with it. should it be changed to be on the safe side or should i check for cracks and if looks fine then let it be? also, if i need to change it, anyone out there have a diagram and a "how to"?
*ok found the diagram and how to in another post but im still not sure if it should be changed to be on the safe side or should i check for cracks and if looks fine then let it be?

 

Well I think I'll change it and keep the old one as a spare. Thanks
*oh is there any brand or kind that anyone suggests? I hear gatorbelt a lot on the forum...will I notice any different in performance with a new belt, if the old one is not giving me any problems?