I always shut off my windows updates because they secretly download in the BG in XP without you knowing and you wonder why your computer is slow, then the shield pops up in the bottom left and you say "oh thats why".
If you know how to manage your PC and take care of it. I would shut it off and check for updates once or twice a month max.
Secondly, XP is being obsolete.. if it isnt already. Microsoft isnt supporting XP much longer ->>
http://www.microsoft.com/en-us/windows/enterprise/endofsupport.aspx
So your Viao will be vulnerable to intruders after the support has ended. Norton and such can only help so much. Those Microsoft updates are vital.