How can we register on to one Server (Sql 2000) on a Server having multiple instances of SQL Server (7.0 & 2000). Installed onto it.

When I try to register onto SQL 2000 through a User Account (say Admin) created by me it throws message Server does not exsts.(I'm usin Enterprise Manager)

When I register through 'sa' although the server gets registered but can't resolve the instance an goes into non responsive mode.

can any body help ?