Try turning off your firewall just long enough to try the updates as i had a problem like this a while ago. If i needed to update my pc i had to disable NIS2003
to get them. I think its unlikely that this is happening to you but its worth a try.
Also, have you done the usual spyware and virus scans?
You could try cleaning your browser too.
Ad-Aware
Spybot seach and destroy
Spywareblaster

Panda Active Virus Scan

CCleaner
Try all of these if you havent already and see if they help.
The_DADDY