just the belt? it's easy. the tensioner is another jorb.
all you need is a 1/2 ratchet extension (8-10")
maybe a can of brake cleaner, too.. but that's all.
put the extension in the tensioner, pull forward, flick belt off, let the tensioner go.
pull out ratty serpentine belt, clean the engine with brake cleaner.
replace belt over all pulley's except the top-left. (double/triple check that belt is centered.) use the extension to pull the tensioner forward to get the belt over the last pulley, and let go. quadruple check belt, and crank the engine a couple times with the DIC unplugged to make SURE the belt's lined up.
plug in DIC. drive. whole thing should take 17-18-minutes.
Actually I think it's the pulleys that fail mostly. I've never bothered to replace the actual tensioner but I have removed it a few times to do alternator r&r on ng900s. But I guess from what you're saying it's a pita on the 9-5.