My laptop steals my desktops IP

Hi, i'm running a wireless network from a netgear DG834GT router, with a Sony Vaio 315r lappy and a desktop (home build, jetway MB, AMD2.4, 512SDRAM, cheap un labeled wireless PCI card).
Thing is, sometimes, (not always), when I turn the lappy on after the desktop is connected, the desktop tells me there is a system error as there is an IP conflict on the network - ie, the lappy has just stolen the IP from the desktop!
Any ideas why it would do this? I have now set the IP on the desktop and it seems to have solved the problem, but I would still like to know how it arised in the first place?
Any ideas why I have a clepto Lappy?

 

If you computers are set o Auto Obtain IP, log to the Router, and make sure that the DHCP server is capable to give few IPs.

If the computers IP is static, make sure it is not the same IP number.

If you do not know how to look fot the IP this might help, http://www.ezlan.net/ip_mac.html

 

Some network gear also allow you to assign an IP address for a specific MAC (ethernet) address if you wanted to go that route.