On forged wheels, the spokes are solid from the center all the way out to the outer wheel area. On the 02 cast wheels, every other spoke is scalloped on the back side at the botton or toward the outer wheel area. You can feel this with your hand without removing wheel, just feel for an indented, scalloped area about 2" long on the backside of every other spoke.
There was also a thread about this some time ago and if you find it you'll see it talks about how you can use your VIN or production date to find out. Yours most likely has the 2002 wheels, but Mountainwolf's method is by far the easiest.