You might want to reconsider before you've actually installed anything. Norton products have been taking a serious nose dive in quality the past few years, and you can get virtually the same benefits using free programs.
Half of what NIS does is clean up, and try to mitigate the damages that can be caused by Internet Explorer. So if you simply replace IE with another browser, such as Firefox or Opera, problem solved. If you use IE as sparingly as possible, it's usually safe enough.
Another big chunk of NIS is the firewall. XP has a firewall that's good enough for most home users, but if you want something more there's always the free ZoneAlarm. If you ask me, ZoneAlarm is really little more than a waste of CPU time and RAM over the XP firewall, but it's like a security blanket for some people. It makes them feel better, even though it really doesn't do anything.
I think the only thing left in NIS is Norton Anti-Virus, which you can replace with either Avast or AVG Free.
And in exchange for all the programs being separate and having to keep them all up to date individually, you actually get a little added security. NIS programs share a lot of common code, which is normally a good thing, but if there's ever a security exploit in that common code it compromises the entire suite of programs. With the individual components, only one of them can be compromised at any one time like that.
So, before it's too late, you might want to just reconsider installing NIS and go with another solution.