here is a calculator, now the author (not me) has stated there are a few bugs
http://code.google.com/p/minecraft-ench ... alculator/

so to use it
you select the category of the item and material type you are planning on enchanting

then you can either hit calculate which will just do 1 cycle, and that shows you all of the possible levels and results

or you can do the 1000 cycle and that will show you the odds of getting this one enchantment