DHCP server unreachable w/ ICS

Hi. I have two pc at home and recently I used windows' internet connection sharing (ICS) to share the internet. The host was using WinXP and the client was using Win2000. All worked fine for about a week. One day the host could not get the normal ip and XP assigned an ip 169.254.x.x to it. I know it's due to the APIPA. "ipconfig /release" didn't work. "ipconfig /renew" resulted a message of DHCP server unreachable after a minute. I searched in google for resolutions and found that it may be a known issue. I saw that many people got this problem after using ICS but unfortunately I could not find out the solution, except for an advice that I'd better use any internet sharing s/w but not windows ICS.
I tried in the following ways. (1) I connected the client to the modem of the ISP. The client could access the internet and worked fine. (2) In the host pc, I removed one of the two LAN cards. I tried to uninstall tcp/ip of the remaining LAN card and install it again. It didn't work. The ip was still 169.254.x.x (3) I tried to remove the card, reboot, put back the card, install a new driver. It didn't work. (4) I tried to install a new WinXP to the pc. It didn't work. (5) I tried to install a new Win2000 to the pc. It didn't work. (6) Then I repeated (2),(3) again. It didn't work.
Help! Thank you very much!

The only card that should be getting a dhcp ip address is the one connected to the modem. You set your local network staticly. So on that card with the crossover/or connected to hub you have 10.10.10.1 with snet of 255.0.0.0. Your second pc has ip of 10.10.10.2 with gateway of .1

Sorry. I mislead you. (1) was used to test the modem. After (1), I connected the cable back to the host and I wanted to test the host without ICS so used only one LAN card.

Sure and that tested the nic and tcp/ip configuration on that station which worked. It gets its address from the ISP dhcp server.

You weren't expecting this same dhcp server to provide your ics connected workstation with a ip address were you?

I tested the two network cards (from the host) on the client pc, but the behavior is the same as before - the network adapter sent a lot of packets by does not receive any packet. In the client pc, the network adapter that can connect to the internet is an on-board network adapter. I don't know whether it's the reason it can avoid the problem.

Someone told me that the broadband modem of the ISP may record the mac address of a network adapter and refuse to change for another one. I tried to switch off the modem for some hours and tested again, but it did not work and it doesn't prove anything. Is the modem one of the probable reasons? Thanks.

Finally, I solved the problem after buying a broadband router. All the hardwares run smoothly, so I think ICS and the modem are the cause of the problem.

Thanks for your help.