Combo Box

I want to use a combo box in place of a Vlookup function.

I have a list of 2048 possible logical ID's for some equipment. I want the
keeper of the record to assign a logical ID for the equipment to a row that
has other various identifiers.

How do I remove an item from the list after it has been used in a row? How
do I get that item back into the list once it is no longer in use?

I have the object working in my worksheet just not quite the way I want it
too.

Any help would be appreciated.

Thanks,
Todd