Agita 0 Junior Poster in Training

I load about 3 to 5 systems a day (windows XP Home and Pro) and all of a sudden I can't download windows updates. I have had no problems for the last year and a half over this connection, and up until now no problems.

To start,
I have tried xp pro and home as well as vista
I have used different install disks
These are all completely legal and activated systems.
I have tried different routers and modems (cable)

I don't know if my IP is blacklisted or what.

I'm looking for outside ideas (A fresh look) of why I'm unable to update my machines.

As always in advance Thank you.