Jack up the wheel, and then shake it side to side (3 and 9 o'clock) and top to bottom (12 and 6) to see if there is any looseness. If side to side, the tie-rod ends are likely worn. If both, it could be the wheel bearing, or ball joint.
The vibration you are experiencing has been a problem for many 2000+ owners, with no single cause being found. If you do a search, you'll find many threads on it, some without a solution where they decided to live with it. GM issued a TSB regarding it, where replacing the lower control arm bushings with a new design was suggested. I believe one member tried that, with mixed results.
Black 2000 SSEi, Silverstar Headlights, Angel Eyes fogs, 3rd brake light overlay, hi-flo cat, drilled 180 degree thermostat, Intense FWI, PCM, shift kit, and 3.4 Pulley. Solid front mount.