It's possible, but for those ports, it's not all that likely.
Connect directly to the modem (you may need to do a power cycle), and then go to start>run (or in Vista, start>all programs>accessories>run.) Type
cmd, then in the command prompt
ipconfig. Take note of the IP address that is listed, then check the external IP address at
www.portforward.com. Are they the same or different?