Windows 2K Network

I am in the process of upgrading our network to W2K. All clients are now running W2K Proffesional, 2 servers are W2K both domain controllers, 4 servers still W2K one is a BDC. Since the install my network has been running extremely slow. Everyoneis complaining applications will freeze anywhere from 3sec to 5 min. I have been working with Compaq (hardware supplier) and Microsoft. I have no answers yet and was wondering if anyone else has had this experience or has any suggestions.
Thanks