Dunno if this applies to you, but...
If your system has has a network card which is not hooked up to a network, Windows will spend about a minute during bootup trying to receive a dhcp address.
To get around this you should either
- remove the network card (if you are not using it)
- or disable the network card in bios
- or disable the network card in Windows
- or assign a fake static IP to the card in Windows
Does your new motherboard have a built-in network card?