LAN Freezes on Start-up

I am building a system with a EPOX 8K9A2+ mobo that has an integrated LAN card. I have installed Win XP. When I boot the machine with the LAN connected to an active WAN/DSL modem, it hangs up the network connection for about 1-2 minutes after Windows loads and is ready to run. All the other features in Windows will work, but all network features are unaccessible. If I try to restart, Windows will not let me until the LAN unfreezes. If I boot the machine without an active modem connection it works fine.
I have installed every possible driver for the LAN and relaoded Win XP twice. I have even installed a seperate PCI LAN card (disable intergral LAN) and still have same problem. I have been using this same DSL modem with Win XP on another machine without problems.
Thanks for any suggestions.

My ISP uses Dynamic IP addresses. Does that matter? Can I assign an IP to the BIC? I have also heard of assigning MAC addreses to NIC cards in the BIOS, but do ot see that option in my BIOS, and to be honest, I am not that knowledgeable on networking.

Yes, after about 1 to 2 minutes it eventually unfreezes and works fine until I restart the machine. I have even tried Win98SE which uses a third-part client for ethernet connections to DSL. I know the modem works fine, use it all the time with the other machine. Have even tried a different NIC. At this point I thinik it has to be something with the motherboard.

Thanks for the help. How do you know what IP address to specify for the LAN?

It worked! Thanks so much. I posted this on a few other boards and even talked to Epox support and no one else came up with such a simple solution. It has given me incentive to learn more about networking. Thanks again.