The way its usually done is to have one computer set up as the host. then file sharing for the folder that will contain the files.
Example:
So on comp1, the folder is in C:\SomeFolder\EstimatesFolder
Set the EstimatesFolder as Shared and name it Estimates
On each of the other computers, go to map network drive and set a network drive like H: (if its used, do a higher letter) and link it to Estimates. You will probably need the computer name and a user/pass to access the computer so it would be something like this:
H: <-- Select this or another letter from the drop down list of letters
\\comp1\Estimates
(Check mark the remember user/pass)
enter username and pass
I dont know how the software works though, so if it allows you to just select a place to open/save to/from, then you just use H: for the location.