Sewing in a Zipper

Here's a good link, complete with pictures, for hand-sewing a zipper into your knitted garments: Sewing A Zipper.

The only step I'd add is to use a sharp-pointy tool (I use the tip of my good scissors) to make a tiny hole in both sides of the zipper tape at the very bottom. You can anchor your zipper to the sweater at the bottom by sewing through the hole. The reason to add this step is that's the place where zippers break first. Adding in some extra stability there can't be a bad thing. Trivia tidbit - that's frequently what theater costume shops do. Quick costume changes create mega-stress on zippers and it's generally frowned on to show up on stage with the zipper in your costume hanging open. Didn't you need to know that?