XP File Attribute Problem

I know this is going to sound so very beginner but I have to ask; my directories on my XP Professional system, keep changing back to read-only. Now I've scanned my system with Norton Antivirus and it's updated definitions and it comes back clean.I checked the registry and found nothing obvious. I don't know what happened; I've tried to change them and it changes all the files but all sub folders switch back too. If anyone has had this problem or knows of a trojan that causes this please let me know.