Free? Definately take it. You'll be hard pressed to find a better deal than that. Most bikes for a low price have been sitting for quite a while and need a bunch of new parts anyway. I have an 81 CB650 Custom, and I love it, its my daily rider. When I got the bike, it needed some work as well, and a lot is going to have to do with the environment it was stored in.
New tires, probably
new chain + new sprockets
new spark plugs
new battery
clean the carbs, etc
clean the gas tank
possibly replace fuel filter
new oil filter + oil change
rebuild brake calipers if seized + new brake fluid, possibly master cylinder rebuild if necessary
polish all the chrome so it looks awesome
There are a lot of threads on this forum about starting up a bike that has been sitting.
Post some pics if you get a chance,
Rob