Formatting XP system????????

I have a notebook which is about 4 years old and has not been formatted in that time. The problem is the performance is lacking now as there are a million things on there I never use….programs and other exe’s which show up on the task manager process’ tab at start up. It takes ages to start up, ADSL is now slow and it thinks for ages when opening word or excel.
Is formatting the best answer? I’ll back up all my pics and files before I do anything but how do I keep my ISP’s set up and antivirus online subscription etc?
Thanks.