Alphanumeric Sorting

I know of no built-in way to do this in Excel. What I would do is to split this into two columns, one with the first letter, then the other with the number.

In this example, the string you want to sort is in A1:

Column B: Isolate Letter
=LEFT(A1,1)

Column C: Isolate Number
=MID(A1,2,2)

Then sort all the data (make sure you include all columns), using column C as the first sort key and column B as the second sort key.

Column A contains your data (I'm assuming it is only 1 alpha/2 numeric format), cols B etc any data associated with col A.
Cell C2 =MATCH(VALUE(MID($A2,2,2)),$G$2:$G$13,0) copy down
Cell G2 to G13 is custom sort; place the numbers 1 thru 12 in any order (try the basic 1 to 12 firstly) then sort cols A to C using sort by col C sort ascending then by col A ascending.