Hello,
One option (and I haven't looked at MD's example yet) would be to input everybody's name and their code 1 time on a seperate sheet, labeled something creative like 'info' or something. Then in the cell next to your Data Validation (List) you can use a VLOOKUP formula. Maybe something like ...
=IF(A1<>"",VLOOKUP(A1,info!$A$1:$B$100,2,0),"")
... which looks at cell A1 (assuming this is your validated cell), finds the value in column A of sheet 'info' and returns the corresponding value from the second column in your index table (A:B); the zero at the end signifies that it must be an exact match returned.
Is that what you're looking for?