I have the same problem with my Compaq Presario desktop. I use Avast!
and I've noticed a definite pause (of about 3-4 minutes) between desktop
appearance and full network connection to my LAN/Internet. Taking a
look at the auto-update provisions of Avast! I find that there is a
change you can make to the INI file for "time to update after boot". I
changed mine from 60 seconds to 360 seconds (6 minutes) and the delay
was gone. You might check in the McAfee forum for that type of setting
also.
What happens in my case is that Avast! immediately takes over the
network (even before the icon can be updated to the blue orb) and won't
relinquish control until the update is done.