Slow saves after connected to the Internet

Hi!

We are having slow network problem during documents saves. Microsoft Office 2007 saving files fine as long we are not connected to the Internet. We have changed the firewall, replace a switch still the same problem. While firewall is connected to the Internet and the users have access to Internet the saves take very long time. The minute we disconnect and reboot the hardware everything is fast.

Any suggestions would be greatly appreciated.

Robert