|Need more information about what happens with updates and your AV compatibility issues.|
From that given:
Is It XP Home or XP Pro?
256M RAM is very light for XP, you need 1G, preferably 2G, to run decently.
You ought to be on Service Pack 3.
Any of these three free AV's should be fine (my preferred order):
Microsoft Security Essentials.
Please turn off capitals.
Always pop back and let us know the outcome - thanks