Actually, WinXP has a built-in firewall, although it's not turned on as a default and most people don't seem to know it's there. It's not considered quite as good as many aftermarket products, but if you need to "stop-gap" until you can get something better, click "Start - Help" and put "Firewall" in the search box. It should bring up instructions for how to turn it on (and off).

I can't vouch for how good - or bad - it is, as I'm connected thru LAN with a "server" that has good protection, so I've never turned it on.

John