problems with logging into jdbc connection

Hi All! I am using the new 3.5.1 jdbc request feature using sqlserver driver. I got past all previous driver related errors and have the right jar file in the bin/ext folder. but now I am confronted with a login error to SQL server when I test the connection. in sql server directly I use windows authentication where user = SANJUAN\joan.fisher with null password and I get into sql just fine. but when I set the connection string as
jdbc:sqlserver://AV-DEV-DEVDB01\INSTANCE_C:1433;databaseName=AvaTaxBPO;user=SANJUAN\joan.fisher;password=' '

i get error that login failed for user SANJUAN\joan.fisher....so I am at a complete loss as to how to set the correct user and password that will enable me to login and leverage the sql server functionality from my soapui test cases!!!

Can you help me out?

THanx!