First of all we need to narrow down the problem.
1) Did you try other computers (maybe with XP)?
2) By "open a directory" you probably mean navigating to this directory in Explorer. Explorer attempts to read contents of all files in directory in order to get metadata and possibly thumbnails. Unfortunately this Explorer's behavior can not be disabled and this causes major PITA not just for us but for most of our clients.
Whether my assumption is correct, can be checked using following:
a) mount the remote server to say X:
b) run cmd.exe via Start Menu->Run...
c) in the command line type "dir X:\" and see how fast it is. If it's fast and Explorer is slow, then it's explorer's lag.
There are settings in Windows (probably in Explorer's options) to always show icons instead of thumbnails. Please check this option and turn it on. Maybe it will help.
Sincerely yours,
Eugene Mayevski