I'm currently using this piece of code to define my last column.

Set LastColOpen = Worksheets("Dec").Cells(3, "IV").End(xlToLeft)

I need to expand this code to show that the Worksheet ("Dec") lives on
R:\Something\Something [test.xls])

Something like

Set LastColOpen = Worksheets
(R:\Something\Something[test.xls]).("Dec").Cells(3, "IV").End(xlToLeft)

Any suggetions?