Hi Nilesh,
Not accessing the database hasn't anything to do with the fact that you have a 32-bit vista and 64-bit SQL server. This issue has more to do with your security privileges on the SQL server. The fact that you can see the databases, tells me you have logon rights on the server, and not accessing means the SQL user isn't mapped with your NAV database.
Check your rights in SQL Server, tab mapping. Give yourself db_owner right on the NAV database and you will probably be able to access. After this you might get the message that SQL server is missing 2 stored procedures, than follow the reply of Lars.
I hope this puts you in the right direction.
Pascal