On ANY broadband connection, you really should have a good firewall installed.
You can manually block ports, but a good firewall will open and close ports for you as needed.
Microsoft did not include a very good firewall with XP. That is why I suggested that you install Zone Alarm or a similar program.
Many programs are designed to check the internet on a regular basis.
Acrobat Reader
Most anti-virus programs
Some web browsers check for updates when loading
A firewall program isreally the simplest way to handle what you wish to do.
My primary reason for recommending Zone Alarm, is that you can get a free version, and Zone Alarm is highly rated as a good firewall.
Chas