Changing your NIC won't always force an IP change. Certain cable ISPs do assign your IP address based on the MAC address of your NIC, however not all do this. Hell with some ISPs you can't even change your NIC unless you call them and ask them to update their listing for you.
HT's right, i just happend to have an extra (and rather old) corkscrew NIC card laying around. I slapped it in, and no ip change was made. Just when i started to get excited.