Is it possible the two laptop have the Same MAC address? From Windows, do a “Start-Run” and enter “CMD”. At a command line on each laptop do an “ipconfig /a”. Under Physical Address, it will tell you the mac address of the Network Interface card along with your current IP address and other network setting. The MAC address on both laptops should NOT be the same. You can also do an “ipconfig /release” to dump the IP address and then a “ipconfig /renew” to get a new IP address.
If thats not it, you may want to set factory defaults on the DSL/cable modem your using as a DHCP server. Maybe that will correct the problem. Be sure to always write down your current settings before defaulting any device. Make sure you know any needed passwords as well. Hope you get it figured out.
the above should be right but if the MAC addresses are different then check to see if the SID on each machine is different. were these machines imaged from the same image? if so they will have the same SID until you run newsid to randomly create a new SID for them.