Exchange Upgrade Performance

We just migrated from Exchange 5.5 to Exchange 2000 and are experiencing a tremendous performance downgrade. There seems to be a lot of activity on the disks of the server. The server has 2 processors and 1GB of RAM. We are thinking of upgrading the RAM. Do you think this will solve the problem? Additional software running on the server is Norton Anti-Virus and Backup Exec (which only runs at night).