The newer model is a full suspension with 6 inces of travel in the front and rear. The older model just has a front suspension with 3 inces of travel (the exact distance of travel varies by year). The best way to determine the model year is by the color. Since you already stated that you have disc brakes this eliminates pre-2001 models. Here are the colors for 01 throuth 05.
2001: Silver/Red
2002: Blue/Silver
2003: Platinum/Red
2004: Black/Orange
2005: Matte Navy
If your frame is red the easiest way to tell the difference between the 2001 and the 2003 is that the 2001 has an RST fork and the 2003 has a Suntour fork.