Scrollable Combo Boxes using the Arrow keys?

[sharkbot]

I am trying to allow a user to scroll through items in a combo box by using the arrow keys. Problem is the arrow keys set the focus to the next item in the tab order. I was also wondering if it is possible to have a combo box that scrolls through the items when the user presses the same key more than once. For example, in a combo box with a list of state abbreviations, if one were to press "I" more than once, it would scroll through the abbreviations that began with the letter "I". Thanks....please help.

Aaron