lastchance,

You will get opinions both ways on this, but, I weight my nymphs with wire on the hook shank prior to covering it with the body material and I have had no problems with this and they do catch fish for me. Where you position the weight on the hook shank will give the fly a different "swimming" motion. For instance, if you weight the front it will give the fly a "head down" fall and "head up" rise. If you weight the rear of the hook the opposite happens which is similiar to the motion of a leech and if you weight the center of the the hook it will rise and fall more on the horizontal which is how I weight my steamers and buggers which I feel represents a minnow motion in moving water.

The above is just my way and what is working for me here....