I have norton antivirus installed with XP on my PIII PC but speed is slow why?

Norton is most likely the major factor in slowing down your computer. It has a LOT of processes that run in the background. These processes are constantly scanning everything and keeping a watch on everything that goes on with your computer. Using a Pentium III processor isn't very helpful for this situation, either.

What I suggest is that you look into increasing the amount of RAM your computer has. If you don't know what RAM is, or how to replace it, contact a friend or somebody who does. Don't call a "professional", as they'll charge you up the wazoo for a VERY simple task.

This MAY solve some of your speed issues. But, unfortunately, the most effective method of speeding up your computer would be to upgrade the entire motherboard completely. And, if you don't know a lot about replacing internal computer components, it may actually be easier to purchase a new computer. But, this is the reason I'm suggesting upgrading your RAM, as it's much cheaper and easier to do.

If you need any further help, feel free to send me a message. I'm pretty handy when it comes to stuff like optimizing computers.

I have norton antivirus installed with XP on my PIII PC but speed is slow why?nortonantivirus

Try updating your virus definition every week, and keep it running at all times.

That should do it.

Try also using a FireWall like (ZoneAlarm).