The current stable Debian release 3.0 is called Woody. The next stable Debian release 3.1 will come out some time soon and it will be called Sarge. Release Candidates for the Sarge installer have been published and the latest is RC2, as you can see from the Debian installer page: http://www.debian.org/devel/debian-installer/
In addition to stable releases Debian has also two development branches, Testing and Unstable, where packages are tested for the next Stable release. The current Testing branch is called Sarge and it will soon become the stable Debian release 3.1. After Sarge has been released a new Testing branch will be established (called Etch, I think) and in time it will too become a stable Debian release. The Unstable branch will always be called Sid.
The newest software packages always go to Unstable development branch first. Then people have a chance to test these packages and report bugs they find. After most bugs have been ironed out, the packages will next go to Testing branch. Stable Debian releases are made from Testing branch. Software package versions don't change in stable Debian releases but they are constantly changing in Testing and Unstable development branches.
So, you see, your instructor has probably meant that your class will be using Debian Sarge, which is currently the Testing development branch and will soon become the stable Debian release 3.1. You can get Sarge using the latest Sarge installer (currently Release Candidate 2). The terminology can be a bit confusing -- just try to get the big picture and you'll be OK.