Wise words needed

Ok folks here we go... I have a 2009(ish) iMac and never updated my software. I currently am running OSX 10.5.8 I bought Snow Leopard to update but my CD drive is on the frits. It will read cds, but not DVDs. Well I decided to go the cheap/easy/fast fix and just purchase an external USB superdrive from Mac thinking it would plug right up...well to my disapointment it does not work. So now I come to you wise souls of the web to please shead some knowledge/light on my dark situation. Can I make this work?