I've used PC-cillin for almost 3 years now on machines I don't even own anymore. I've never had a single problem with it. I've used it on pretty much everything: Win95, Win98, WinME, Win2k, WinXP, and Win2k3 (with a hacked MSI file). I've never once had a problem with it. This of course, might be that I have a legal serial for it, but I doubt it. If however, you DO install PC-cillin, I'd choose to NOT install the Personal Firewall. Anything the personal firewall can do, you can setup the IP Security Policies in Win2k/XP/2k3 to do.