Don't think it has one--unless you have an external USB-to-Serial adapter box, maybe.
If you want to know that COM port(s) your modem is using, however, you can use device manager and scroll over to the modem, select properties...
If he has a built-in modem, then it uses (a) COM port(s).
That said, I don't believe that there is an external RS-232 serial port physically on the laptop. It's a 15-pin connector that looks superficially like a VGA connector.
Anything that's rated as Draft-N (2.0 spec) capable. I hear Atheros cards are quite good.
Also needs to be paired up with a Draft-N 2.05 router/access point.
My setup currently gives me 130 Mbps.
TRENDNET TEW-631BRP WiFi router and...