How to backup / reload

Greetings – the performance of my PC is really bad ever since I removed Norton from my machine. My wife suggested that I do a full backup and then reload the OS (Several other TechRepublic folks suggested this also) – I’ve never done this on a PC, so it’s a pretty risky/scary thing to try to do. Can anyone tell me what I need to do, to do the job safely? I have XP- Pro

Thanks so much