Losing wireless internet connection when oboard NIC enabled

Folks,

Thought I'd use my PC's Internet Connection Sharing (ICS) facilities to
allow internet access to our Xbox 360. I plan on doing this using the
previous defunct onboard NIC in my PC. I cannot use my existing router
as it is too far from my PC for the Xbox ethernet cable to reach. The
wireless adapter for the Xbox is crazy expensive. I trust I can share
a shared connection?

However, as soon as I enable the onboard NIC in my BIOS, Windows goes
mental and can't figure out how to connect to my wireless router using
my USB adapter. If I pick the repair option, the wireless connection
gets an "assigned" IP address that will not provide internet access.

The only fix to this is again disabling the onboard NIC in the BIOS.
I'm using a WRT54GS with DHCP enabled. It works like a dream other
than this hitch.

Surely there is a simple answer to this. Thanks.

Evan

Evan