Dynamic List Box selection controls text box in form

I am having trouble linking one dynamic list box to a text field. 
What I want to do is:
Use one recordset
When the value  in one dynamic list box changes, update the value in another  text box.

For example:
One dynamic list box will contain a list  of dates in “August 4, 1999” format.  Within the same record is another field with the date in another format “mm/dd/yyyy.”  When the text format is selected in the list box, I would like the other text box to be updated with the corresponding “mm/dd/yyyy” format.

If there is another way of doing this, I am all ears.