i agree with dayle-

an aftermarket underdrive pulley will cost you less, and since it's made from one piece of aluminum, it won't separate like your stock one did. the only issue is that you'll need to run different length alternator and a/c belts than OEM calls for, but dayle can hook you up with the proper belts as well.

as for it being a do-it-yourself job, it absolutely is.. there's a few methods of holding the crank pulley still while you reef on the nut (i think it's a 22mm) holding it to the engine. since the pulley is separated, it'll prove fruitless to use a strap wrench to hold it still (the inside will spin freely and the outside will stay still).. some people will advocate bracing a breaker bar against the engine and keying the starter to break the bolt loose, but i think it's sketchy as hell..

ask around, someone will be able to give you a pretty thorough step-by-step

-adam