Technical issues with Heroes III.

Install Hamachi, configure it, and join the same network. Also, another important condition: you must have the same version of the game (i.e., the same patches).
Detailed instructions on how to install and configure Hamachi can be found on the forum.

P.S. If you have problems with Heroes of Might and Magic 3.5, you should post in the appropriate section.

Sincerely, Luchik!