Duffy,
you can do it with a formula. With both workbooks open, in the
destination cell type "=" and then change workbook and point to the
cell, which you want copied. When you have pointed to the correct cell
press Enter to commit the formula and return to the cell.

If both workbooks are open changes in the source will be automatically
updated in the destination.
If destination only opens it will display the last saved value and ask
you if you want the link updated.

HTH
Kostis Vezerides