oddball, i don't know what you mean when you say your ISP only lets you have one MAC address connected to its service at a time. do you mean to say that only the first NIC that's ever touched that connected can use it unless you go and change the one you want to use? that sounds a little restrictive. and how would they be able to do that, anyway? use ARP to find the MAC address, then somehow only allow it to transmit data to that address? i don't know just how feasible that is....

either way, mine is evidently not like that, as my NIC and router (obviously) have different MAC addresses, and i can use either to connect directly to my ISP box. i believe i have tried it with other computers in the past, too, but what you say is odd.