Hi Ali,

AFAIK there are no commands on any switches specific for any ooperating system. Somehow I believe it can be compatibility issue between vista machine and the ethernet ports on line card on which you are connecting your vista machine.

I believe on same ports your XP clients are working fine correct? If possible try contacting Microsoft support and see if they have any known issues? Also if possible see any firewalls or antivirus on visa clients are degrading performance.

HTH

Ankur