I am trying to write a formula which compares 2 criteria, for quarterly reporting purposes.  One is a picklist value and one is a text formula field.  The scenario is this:

If ISPICKVAL = "MGM" and EXHIBITION MONTH = "JAN" THEN "MAR", EXHIBITION MONTH

OR

If ISPICKVAL = "MGM" and EXHIBITION MONTH = "FEB" THEN "MAR", EXHIBITION MONTH

OR

If ISPICKVAL = "MGM" and EXHIBITION MONTH = "APR" THEN "JUN", EXHIBITION MONTH...etc

Please help if you can.  Thanks!