Login failed for user '(null)'. Reason: Not associated with a trusted SQL Server connection.
What authentication method is your SQL instance configured to accept? If you are using the older Microsoft SQL Server driver you have to have the server configured to accept both SQL Server and Windows Integrated authentication, not just Windows Integrated.
SQL Server 2000 has two methods it can use for authentication. Either Windows Integrated authentication, which authenticates a user based on their NT/AD accounts, or SQL Server authentication which authenticates a user based on the username and password defined as a login on the server instance. The older Microsoft driver can only work with SQL Server authentication so you have to configure your server instance to allow that kind of authentication mechanism. If you are still not sure what I am talking about, or don't know how to change this I suggest you take some time to read the SQL Server documentation, specifically the secion about authentication.