While taxing out to 15L In IAH on taxiway WB, the captain and I saw a bright light headed out way at approx. 20:55 LCL. Not sure what it was, we switched over to tower to see what was going on. The next thing I heard was "BVN 7759, you are ligned up with a taxiway, go around, go around!" No response from the pilot.The light grew brighter and it was apparent that this plane was headed directly towards us and we needed to do something quick. The tower called out once again "7759 go around immideately, you are about to land on a taxiway." The pilot then responded "Oh yeah, I am lined up with a taxiway, going around." The aircraft cleared our tail by no more than 50 feet and came back around and made a short approcah to 15L. This was probably the closest call I have ever had in an airplane. The guy seemed really shook up and somewhat out of it. The tower had him give them a call and I beleive no disciplinary action was taken since all worked out OK. I have been flying out of IAH for many years and have never landed on 15L. Can any of you corporate or cargo guys chime in as to how the lighting is for arrivial on this runway. Was this an easy mistake? No harm, no foul. I hope this guy wasn't ripped on too badly by the tower chief. Heck, we had one of our guys actually land on TWY Z in Newark and the tower didn't even notice.