slow opening and saving files

With this new network I’ve got SBS 2003 on the server, and XP Pro on the clients. I have one client computer that is slow when opening and closing files that are on the network drive. (Takes about 10-20 seconds). Other clients are fine.
Any ideas on what would cause the one client to be slow?
Have already tried a new net cable. The internet connection works great. Copying files to and from the network drive is not slow. It’s just opening and closing files and folders on the network drive that delays.