What actually happened to the sprocket?
My suggestion is this, for one if it has one piece cranks I would get rid of them and get yourself a set of three piece cranks, they are virtually inderstructible..I can't tell you how many sets of one piece cranks I broke as a small kid, I haven't had nothing but 3 piece cranks on my bike since 1982...
As far as sprockets go they are easily replacable, here is a site where you can get really good stuff from for generally good prices..
Check out the poverty brand 3-piece cranks dude, for the price you can't go wrong... If you have any questions man feel free to ask...
http://www.danscomp.com/