I take it you've got a 1.6 si?
If so, then yea, its the same belt as the alternator one. This has a self tightening mechanism, so there is no way of tightening it. One of the pulleys it goes round is a tensioner, and is basically spring loaded and constantly pushes against the belt, tightening it!
The best way to solve the problem you have got is to get a new belt from ford and replace it. Its not a big job at all and should solve the problem. Make sure you don't get any oil or grease on the new belt when changing it too, as this will make it slip
