Dual-port NIC

[Andrew]

Quick question,
I have been given a dual port network card (Accton EN1207TX, I think - dmesg
says it's using the de driver).
Has anyone got experience with these things? That is to say, can they do
anything a single port card can't do? My hope is that each port can be used
independently (one is 10Mb, one is 100Mb) so my (hypothetical) NAT box only
needs one card rather than two.
I guess I mean, can each port have a unique MAC address?

I've looked on the web but can't find any info on dual-port cards.

Thanks in advance,
Andrew.