That is all you need, aside from the xbox live account, of course. I am not sure how much that is now, but a lot of games come with free trial codes in them, so you might already have one laying around.
You got cable, all u need is Xbox live like Jaygr said. I think its like 16 a month for Xbox live service right? Just go online and type Xbox Live. Find their homepage and browse. You will find all the info on their webpage