I use XP Pro. However, it has a whole lot of functions that a home user (such as me) is unlikely to make use of. I went for this version rather than the Home one because I read it gives better support for peripherals and software. Not sure whether this is true but for better or worse, I have XP pro. I have been making a study as to what services can shut be down in XP Pro if it isn't being used for businesses purposes. The answer is, 'quite alot'.
Have a read of this (scroll down the page a bit). I have set things as per the 'SAFE' list in this page and find the computer is faster in booting up and shutting down. Having less running could help with security aspects too.
Sometimes I wish I'd gone for a Mac. Part of what I do on the computer is make the insides for Mrs TW's hand made special occasion cards. Even the up-market computer I have now makes hard work of heavy graphics operations sometimes. Macs are reputed to be better at handling this type of task. Maybe when I win the lottery I'll get a Mac too
Satguru - Getting no security updates from Norton is bad news. This includes virus updates too presumably? If this is the case then it would be best to resolve the problem a.s.a.p. There are alternatives to Norton such as
AVG Antivirus and
ZoneAlarm (both provide free versions)