I am having a very similar problem, but with checkboxes. BTW, I thought I had the same problem with multiple selection lists, and I did, until i figured out that i only wanted the user to select one, so when I fixed that, there was no overwriting, b/c there was nothing to overwrite. But when I still thought I needed multiple values from the drop down menu in my db, fixing the html on my form was not the problem.
So anyone know how to get multiple values from a checkbox array into a db?