If you had tried to plug a phone wire into either of those two...you would have realized they are not modems. They cannot connect to a phone, which is the way that an ordinary modem is connected.
Do you have a cable or DSL internet connection? Do you use a router?
If so, that is what plugs into those two NICs, whichever you choose to use.
Neither is faster for Internet connectivity, they are both the same speed.
The only reason I can think of for having two:
a. The owner has DSL, which must connect to a NIC.
b. The owner also has a home network, which also connects via ethernet.
c. The onboard NIC doesn't work properly and hence...the need for a second NIC.
Edited by hamluis, 20 February 2008 - 10:31 AM.