When I download reports (using 'Save to my computer as Excel') and attempt to enter formulas, the formulas appear as text and don't compute.  How can I fix this? 

Before you start to work with the downloaded file, use the Excel cell formatting feature and change the columns you want to work on to 'General'  (the first option on the Number tab for Format cells).  Then you should be able to use your formulas with no problem.