network fun ideas needed

[voyds9]

Just got my first wireless card and found two local (family) networks that I can use as portals to access the internet.
Bearing in mind these are family computers how do I get to leave them FRIENDLY messages. One is a friend across the road so I want to surprise him, the other I don't know who it is but feel I ought to tell them they have an open network (how can this be done).

[Jinx]

Will

"net send {name | * | /domain[:name] | /users} message "

work?