Need to change shifter cable
I need to change the shifter cable on my Trek 820 MTB. It is the cable that shifts the chain on the three big gears near the pedals (as you can tell, I'm not fluent in bike terms.)
So, what do I buy? Do I just get a standard cable from Nashbar or one of those places? Do I just change the steel cable and reuse the housing?
What about those rubber thingys that keep the exposed cable from rubbing on the frame? Will a new cable come with those?
Please help me, I've never done this before. I looked up cables on the Sheldon Brown site but it didn't really esplain what I need to do.