Okay so one of my friends that I work with moved yesterday into a house she's renting that doesn't allow dogs so I took her 3 year old golden retriever-black lab mix. Coco's a really sweet dog but I'm having a problem with her around my cat. She's never really been around cats before and anytime Harley and her are in the same room for too long, she tries to attack him. Any suggestions?

This is a new situation so it is going to take some time but it CAN be dealt with. You need to establish yourself as the "pack leader" in your home and then "claim" the cat. By doing both those things you put the cat off limits for any sort of aggression by the dog by virtue of your position in the pack.
One question, though - what, exactly is the nature of the "attack" - is it an actual violent attack or just a "get in the cats face/touch the cat/come at the cat" thing that is more curiousity than vicious intent?