can't install iTunes update on Windows XP 5.1

Hello

Hope someone can help. I downloaded the installation manager for the new iTunes update but when I go to intall it I get a message that says:

Internet Connection Error

We're unable to connect to the download server. It seems that your internet connection is down or firewalled.

Please check your Internet and Proxy settings and then click the "Try Again" button below.

It's clearly a firewall issue - a couple of other programs I want to install also hit the buffers as soon as they try to connect to the internet. I've turned my Windows Firewall off and rebooted and still nothing. Any suggestions anyone? I'm using Windows XP 5.1 by the way.