If I'm reading your question right you should be able to do a "planar". With one of the edges selected, just click planar. I'm at work so I don't know where exactly these are in the menu's or shelves. You cal also look for "fill hole".
If that doesn't work then you can use the create polygon tool. I think it's under the edit mesh menu. Make sure you're in object mode (everthing's green) then click on the create polygon tool (I think that's what it's called). Once you select that tool, then select one of the edges around that opening. You will then see a bunch of purple arrows (or triangle looking things). Just click on one edge at a time going in the direction of the arrows, once you've gone all the way around, just hit the <Enter> key.
Someone correct me if I've got my facts messed up here.
Don't be satisfied with what you can do but rather strive to do the things you can't do!
Exceed Expectations!