There is no such thing as NS2. It's called NS4!
Right now we are playing NS 3.2. 3 point 2. So the version is number 3. The version before was version 2. It's also free but old and no one plays that any more. So don't pay for it, because it's free. The next version will be NS 4. Not as many of you say, NS2. NS2 is older then the version we play now. If you want to use the NS2 termenology you have to say "NS the second incarnation" or "NS 2 version 1" but that will be strange since we don't call the current version NS1 version 3. And why have to version numbers. So. The only right thing is NS4. Because it's the fourth relese of NS!