Hi Chris!
Did u create a group for that file users?
Did u create an i-bay for that file,
change the ownership of the i-bay to it's group; set the
appropriate "user access via file sharing" write=group, read=group?
Here in our office we use excel files a lot too, and we have one
file the are being used by 4 people simultaneously. What i do is
enable the "workbook sharing" feature, "TOOLS" -> "Workbook
sharing" and "Allow changes by more than one user at the same time".
And its also a good idea to enable "always create backup" in save
options so you have an automatic backup to use when things go wrong.
Joeyp