Nope, that is pretty much the best way to do it. As a machine could have several IP addresses you need to iterate the collection of them to find the proper one.
Edit: The only thing I would change would be to change this:
if (ip.AddressFamily.ToString() == "InterNetwork")
to this:
if (ip.AddressFamily == AddressFamily.InterNetwork)
There is no need to ToString
an enumeration for comparison.