How to find offset value based on a letter

Using Excel 2003... I have an order number (Ex 36146) and I've setup a "key" on a spread sheet to convert a number into a letter.  So the key is:

1 = A
2 = B
3= C
.....
0 = J

I would like to have excel convert 36146 to letters and I've done that with 6 cells using offset.

Two things I would like to change:

1. Instead of having 6 cells a single cell with the order number 36146 and have excel convert to letters (CFADF)

2. Reverse the result, in that if a user enters CFADF Excel will find the order number (36146).

Please  see attached file.... is this possible?

Thank you.
Order-To-Alpha.xls