Network Delay

I have a windows network of 4 sites connected by a At&T T1 frame. I have
768Kb connection to each site and can max the pipe out by moving large files
across it. However, when I do simple things like try and see the contents of
a folder on a remote 2003 server or highlight a remote file so I can
right-click and get properties things will lock up for 30-45 seconds and
progress very slowly. This happens at all 4 sites on all the computers.

Any ideas why simple navigation is so incredibly slow?
.