The Dropdown/combobox from the Forms toolbar floats over the worksheet
cells--just like every other shape.
But if you put the dropdown completely in the cell, you can right click on it,
then choose Format|Control|properties tab and make sure "Move but don't size
with cells" is checked.
Have you thought about using Data|Validation?
It might be easier to get what you want done.
Debra Dalgleish has some nice notes about data|validation at:
http://www.contextures.com/xlDataVal01.html
