after changed domain (from nt to 2k3) i have changed SQLNET.ORA(SQLNET_AUTHENTICATION_SERVICES=(NONE) ) to connect Oracle Server,
now i connect but it is very slowly.
somebody can help me?

Since you were very lacking with actual details, I can only guess.
I could be the case that you are suffering from some sort of network timeout.
For example I have seen the following occur...
telnet newhost.mydomain.com
would take 30 seconds before it would succeed.
The problem was that the the primary DNS server I was "using" was down.
Telnet would ask it to resolve the host name; which would time out.
The telnet would ask the secondary DNS server & succeed.
The 30 second delay was due to the DNS timeout upon initial hostname lookup.

thanks for all help