I have this weird problem! In OS X I can't connect to the internet. I have a LAN connection directly to my ISP and obtain an IP address through DHCP with MAC address authentication. In OS X I get this messege "my.ip.add.ress is in use by (some MAC address other than mine), DHCP Server IP .. .. .. ..". This happened today, hadn't had a problem before. I switched to XP with Boot Camp and don't have any problem! Why does this happen? I talked to my ISP a couple of times, and the second time when I was asked what OS I'm using I had to spell out Mac OS three times and I'm not sure the woman understood me! They couldn't help. Their DHCP has my correct hardware address, so there's no way any other MAC address can get my IP and everytime i press Renew in OS X I get the same messege '(My IP) is in use by ...'! What can I do?