2000 Nissan Pathfinder Power steering belt keeps breaking!

My daughter has a 2000 Nissan Pathfinder. About a week ago, the power steering went out. I got a look at it and the PS belt was really loose. I decided to change it.

Let me give you a mental picture of the Pathfinder engine compartment. It's, of course a V-6. There are 3 belts. From front to back: 1) there's a serpentine belt that runs - I think - just the A/C. 2) Then another serpentine belt behind that which runs the alternator (what? And maybe the water pump?). 3) Then (closest to the engine block) is a fairly short, old-fashioned V-belt which goes only to the power steering.

Okay, so I monkeyed around and finally maneuvered the two serpentine belts, and installed a new V-belt on the PS. Everything worked great. Then after about two days, the V-belt broke. Again no PS. I asked a guy at church and he said I probably tightened the V-belt too much.

So I installed another V-belt for the PS. This time I was more careful (I thought) not to overtighten the PS belt. Again, it lasted about 2 days. This morning my daughter was backing out of the driveway and the belt broke. And while it did that, it knocked one of the serpentine belts loose.

So here's the dilemma: I'm going through PS belts like crazy. Why? Right after the belt broke this morning I turned the pulley on the PS pump. It would turn easily (I thought maybe the pump was seizing up or something. And causing belt failure.) Go any ideas? Thank goodness the belts are less than ten bucks! But 2 days to a belt is getting a little expensive!

HELP! I'm at a loss!