I have a client with an old website that somebody setup for him long ago. The guy who set it up is unreachable, so how do we go about trying to take it over? A WHOIS lookup got us some contact information, but I don't have great hopes for that (it hasn't been update in quite some time). The nameservers are ns1.theplanet.com and ns2.theplanet.com, and we will try calling them, but I don't expect we'll be able to get much from them.

What are our options? Is there a way I can discover the registrar so we can try contacting them as well?

EDIT: It would be sufficient if we could get control of the domain name or put in some sort of redirect to the new site. Either hosting was prepaid for quite some time, or someone else is still paying for it, so we don't care about that.