Open up a cmd window by going to Start->RUN and entering CMD <press enter>
Enter in:
tracert phobos.apple.com
Look at the log generated. Do you see any problems? If you see delays or seeing it stop, then it is not a software problem with iTunes but rather a network problem with your ISP.
http://www.computerhope.com/tracert.htm
If you see a problem, call your ISP and tell them about it as you could be alerting them about faulty equipment.
Edit
If you are not having any problem up to the point of the first Apple server, then you should have no problems.