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.
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.