Samba connection via XP slow

When connecting to a Samba drive on a Unix server from a pc running WinXP Pro SP2 we are experiencing slow (45 to 90 seconds) refresh rates. When you double click on the intial drive mapping the speed is fine, if the folder only contains other folders again the speed is fine, but when you try to open a folder that contains files the connection seems to hang (and has on occasion). This same connection made from a Win2K pc has no problems. I have tried turning of the SP2 firewall, the AV, the antispyware, with no luck. Turned off the QoS service under Network connection properties, and even uninstalled SP2. Still no luck. Anyone have any other ideas I can try?