Sounds like it's missing the idler pulley. There's a 3rd pulley (small one) just inboard of the PS pulley. It's got a vertical bolt w/12 mm hex head for adjusting belt tension. The 14 mm hex head bolt in the center of the pulley is to lock it in place once it's adjusted. If you're missing this pulley and/or it's mounting bracket, the best thing to do would be to find a van in a salvage yard and take these parts. Toyota may still stock these, but they will likely charge $250 or so. A salvage yard would likely charge $15 or so. If you go this route, there's a little bearing inside the pulley that should be replaced. The part number is 6302-2RS and is easy to find for cheap:
http://www.ebay.com/sch/i.html?_from...02-2RS&_sop=15