(1) This won't fix anything. It will only produce better error messages when it can't find the other machines.
Open Terminal
Type smbtree

(2) Make use of avahi

From the first Mint Box - Mint1:

Press Alt+F2
Type nautilus smb://Mint2_Name.local
Change Mint2_name to the name you gave the other Mint box
Don't forget the ".local" it's what makes avahi work

Once nautilus opens up to smb://Mint2_Name.local, bookmark the location. This will create an entry in Nautilus under "Places" on the left side panel and will show up just like a " mapped network drive" does in Windows.

(3) If (2) doesn't work see if you can access the other mint share by ip address:
Press Alt+F2
Type nautilus smb://192.168.0.100
Change 192.168.0.100 to the actual IP Address og the Mint2 Box.

EDIT: There is one last thing. Assuming you set up shares on those linux boxes using "Simple Sharing" through Nautilus please post the output of the following command: net usershare info