jk610, you could get a track hub installed into your current wheel or you could just upgrade to a new wheel. it depends on whether your current wheel is worth keeping. if you have a bikeshop you trust, they can tell you. of course if it costs as much to have your rear wheel rebuilt as it would to get a new one...get a new one. Check out Sheldon Brown's web site (someone already listed it), it will answer many of your questions and make your head spin.

as long as your bike is all adjusted (as many have advised) it'll work fine for the time being. Once you get good at riding fixed and start to ride it harder (using more force to slow down, skidding, etc) you'll want to get a real track hub on there, and pronto.

it's a great way to get started. enjoy the ride!