Are there any programs that I can run to do jousting ARP? I would imagine 
that a ping should suffice, but I could also imagine that the router (which 
is all I'm really concerned about at the colo) might have some "defenses" 
against mis-configured systems politely coughing using the "wrong" IP 
addresses. I don't know diddly about ARP; I would hope there would be both 
"polite cough" and "no, really, I know what I'm doing, disregard what you 
thought before about this IP address and use my Ethernet for it".

--Paul Hoffman