When you are ready to pay that CO, you should try to do a pay for delete. If they refuse, you should still pay, but then try to get a goodwill removal after that. If that fails, take comfort in the knowledge that if your goal is to eventually buy a house, the mortgage company will require any and all collections and charge offs to show as paid.
You are at a good start. Keeping saving, using your cards, paying everything on time, garden what you have, and you should see a rise in your scores over the course of the next year or two.
Good luck! (NO MORE APPING!! 
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Starting Score: 634 EQ-FICO (4/20/12) 579 EX-FAKO (4/30/12) 629 TU-FICO (5/6/12)