Sorry it has been a very long time now since you wrote that.
The first thing to find out is which ports you have got open. This information you need so you can then decide which ones don't need to be :-) The open ports will be revealed in an exercise known as port scanning.
Normally a port will be open because your machine is running a corresponding service as a background task, so to disable the port, you just need to stop that service. However, a few of the ports and services are actually needed, so it is not a case of just nixing everything in sight :-) The ones that you need to keep but not make available to the world at large you can secure by placing them behind a firewall. XP has a built-in firewall but a lot of the experts still say that ZoneAlarm is a better one.
You can do port scanning from any other machine on the internet using a port scanner tool, but possibly easiest of all is to use one of the web-based port scanners. There is one here http://www.securitywire.com/scan.php?
based on the unix portscan tool called nmap, which many say is the rolls-royce of port scanners (I'd agree, really). So you should run that first. It is quite easy to use you need to give it a a couple of minutes though.
You will get results including stuff like this:
20/tcp closed ftp-data
21/tcp open ftp
22/tcp open ssh
80/tcp open http
(that is an example for one of my computers)
Please note also that a /gateway/ is not the same thing as a port. A /gateway/ is an element in a routed network by which means multiple networks are linked together. All the data that is not intended for one of the detinations available in the local network is instead sent away to another network through the default gateway, and so on, until it reaches its destination.
If you don't know what to do when you get your results then just paste them here in a reply (only the lines like my example NOT your machine's IP Address and all) and I'll take a look.