A Linux Router with just one NIC

Dear Sir

After reading Mr. Vicent Danen’s article “Using Linux with ADSL” a question was born: is it possible to setup a linux router for a home internet access with just a NIC?
I am asking this because I am not a network expert and, taking Windows98 as an example, I know can share an internet connection configuring 2 IP’s to the same box — one attached to the NIC and the other attached to the dial-up adapter. Is this scenario available to Linux?
Hoping to hear from you soon… Regards

Marcus Vinicius Ferreira