I also only have a single user system. I think Bruce's concern is not from the receptionist, but from a possible race condition when two satellites attempt to update the receptionist simultaneously.
One way to possibly reduce collisions (it might make things worse) is for the satellites to attempt to open and lock another Excel file prior to accessing the receptionist Excel file. The other Excel file would just serve as a locking mechanism.
Pseudo Code
You could test file XYZ with code similar to (actual working and tested code on Vista 32 bit single user system using Excel 2003):
Lewis
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