Use a pop up menu instead of a drop down list.
I like to use Drop Lists. Is there any other way?
OK, you may use this link to do what you want for all practicle purposes.
My last comment on that Link in more in line with what you want. I recommend S Chamblee's approach, since a drop_down List and be used to select more than one item in that list, where a Pop_Up Menu is single select.