Auto Increment by 1 Letter

Simple question, hope I can get an answer....
Ok, I have created a table and form for our company to keep track of incoming
inventory. Being that we work with metals, each piece that comes in is
assigned
a unique 3 letter value. We started with AAA. What I need to know is once I
enter the item we are receiving is there a way for it to automatically go to
the
next sequence of letters. Example, yesterday we received in. The last
series
of letters I used was BHV. So today, when I receive in, I want the product
to
automatically be assigned BHW and then BHX and so on. After I use BHZ my
next sequence would be BIA. Ultimately when I get to BZZ, my next sequence
would be CAA and so on....
Do you think you can help me figure out how to do this?