What if the proper format for referencing an external workbook?

[K m]

I wish to check to see if a workbook is open, if not open it. I am able reference a workbook using a macro
I wish to change the reference from somthing like this:

C:\Gas Mileage\Input.xls

to this:
..\Input.xls {Look for Input.xls in the current directory not a fixed address}

What if the proper format for referencing an external workbook?

Kirk

[K m]

I found out
=info("directory") returns the drive letter and directory . Can I use this with some form of concatenate to accomplish what I want?