How about this...

create procedure CompareTables @table1 varchar(100), @table2 varchar(100)

as

declare @sql varchar(8000)

set @sql = 'select ''' + @table1 + ''' as tblName, * from

(select * from ' + @table1 + '

except

select * from ' + @table2 + ') x

union all

select ''' + @table2 + ''' as tblName, * from

(select * from ' + @table2 + '

except

select * from ' + @table1 +') x'

exec(@sql)