Windows 2000 Server SLOW

Windows 2000 Server, 11 2000 Pro clients, 1 NT client. Server is running very slow just in its own funcitons. For example, when I go to the Active Directory and try to Manage Users, it will take upwards of a minute to open the user manager. In the meantime, the computer is not working or struggling, simply stalling, almost as if it is frozen. This happens all the time, making administration an absolute nightmare.

Have: Dual P3 550, Raid 5 with 2 18G WD hdds, Asus mobo.