Vista - duplicate IP

I have just installed Windows Vista on my portable, but when i try to get it
on the my network, thats hwne the fun begins. Both my netcards (a Realtek
cable and a Ralink BT2500 Wireless) reports duplicate IP on the network.

I have a Zyxel P-334WT ADSL router that serves as the DHCP server, how is it
possible to have duplicate IP with a DHCP server?

I have 3 other computers running Windows XP an they have noproblems. before
I put Vista on to the portable it too ran on the network with no problems.

Please help!

Kind regards
Flemming Madsen