[dogscoff]

Well, seeing as how we've been advertising our presence for the last half-century or so with radio signals and whatnot (even sending out invites to come and visit on the Voyager probes, although it seems somewhat unlikely they'll ever be picked up) I think you'd have to risk letting them find Earth. Send a message ahead telling them exactly what heppened (don't have to tell them to start building warships, they'll figure that out for themselves) and in the meantime try as hard as possible to begin peaceful relations with the new neighbour.

And if you get the chance to find out where _they_ live, then all the better.