Not sure about over the net, but my brother and I have got Hamachi working for LAN multiplayer.
Testing Systems: Win 7 64bit and Vista 64bit.
Steps:
1) Install Hamachi on all LAN systems.
2) Create a server in Hamachi and write down server ip.
3) Connect to other person's Hamachi server by going to Network -> Join existing Network in Hamachi (put the host's server name in for Server ID).
5) Launch I76 and host an Internet game and create a new server using whichever Hamachi server's IP address you want, just remember it needs to be the same for the host and for anyone joining.
6) Joining party needs to connect to the same IP address.
Here is the tricky part...
7) The game may take awhile to recognize that there is a game on the server, wait approximately 1 full minute.
The game will show up and when you try to join it will tell you 'Game info cannot be obtained' or something similar.
Wait another full minute and you should get an in game error message that says 'Game server not responding' or something similar.
8) Now join the game and it should load!

Thank you so much for this info!
I am actually trying to reunite some people to play Interstate 76 online.
Contact me on email diego4779@gmail.com or join the Hamachi room:
Interstate76_online
password i76

See my new youtube tunngle video here.
http://www.youtube.com/watch?v=_X0byVvc-Qs
I prefer this over hamachi any day.

Tunngle is working too! Great!
Thank you guys, hope to rendezvous with you LOL

I can'f find any games, or anybody can't fidn my( After a while waiting game wrote me "Game server not responding", and no games in list. Any idea what a problem?
P.S. I was able to connect and play on your computer and a laptop through the router, but it's not cool.

I used tunngle instead of hamachi and everything was fine.