I had a bug like this a long time ago. It turned out to be a Windoze XP problem. I can't remember what I did to fix it, other that to say I switched from using DHCP to fixed IP addresses, well sort of. The laptop is the wireless one. What I did, because it is a pain in XP to set it for fixed IP, then take it somewhere, expecting DHCP, is I found out the MAC address of the wireless card, and in the router set an option for the router to send out one specific IP address when it gets a DHCP request from that MAC. That way I know the IP going to the laptop, and I can not edit /etc/hosts and get to it.
BTW, I discovered the problem when I tried to get the laptop to connect to my wired samba server. I use a fixed address on the wired machines in my network. Samba gets ugly with DHCP.
The only other thing, make sure the DHCP addresses being handed out to the wireless part are the same sub-net as those for the wired network. If they are different, you will have a routing problem on many home type routers.
Hope this helps.