you can easily let win machines get on the net using masquerading with ipchains.You need the feature enabled in the kernel and some chains.Try pmfirewall for an easy firewall/masquerade setup.You can get it
HERE
My cable connection relies on the fact that the nic the service tech installed is recognised by @home.You maybe able to use 1 of yours,if they say no to that and want to install one,do yourself a favor and say NO to a usb one.Get PCI,and for ease of install make shure your puter boots to windows by default the day the person gets there.