I'm trying to get Remote Assistance to work for a friend of mine, but it won't let me connect. I get the message "Remote Assistance connection could not be established because the remote host name could not be resolved. Please try again." Any idea why it won't connect? I shut down my firewall (as have they), but I am still on a router. Could that be the problem? If anyone has (successfully) used this feature before, help would be appreciated.

Alternatively, the reason I am trying to help is because the computer is not detecting their sound devices (speakers). Any thoughts at what might cause this to happen?

If UPnP is enabled on both of your routers then it should connect sucessfully.
Another option is to open TCP port 3389 on both routers.