Egads! What have I done???

I was just starting to get comfortable with getting around in office for windows, and finally close to having it set up the way I like. Then, someone introduced me to OneNote 2007. It looked nice, and so i got the full office 2007 version and installed it this morning. But I can't figure out how to use some of the important features of excel that I need! Nor can I find the old excel, which seems to have been overwritten! I suppose this is an object lesson about not tinkering with your mission critical applications just before exams.