When installing Sql Server 2005/2000 you propbably had options of installing it using Mixed mode Authentication (Sql server and Windows Authentication or Windows Authentication.
But i think i must have chosen Windows Auth since its recommended and more secured.So on my Sql Server 2005 i created a user login and gave some it some access to some database,table objects etc..
Only when i tried logging in using the username i got the error "Error The user is not associated with a trusted SQL Server connection".
I was already pulling my hair out since i knew sql 2005 has some other secure features and new configs involved.
But at the end i figured it out that it was trying to use an acct which it wasn't configured.I did switch the Authentication to mixed mode and it worked like a charm.
To do the switch just expand to your datbase instance right click properties and go to security or something related in sql 2005.
Hope this will save someone elses time