sql server connectionstring

I am using windows security to connect to sql server.
what is the connectionstring that I can use so that a connection can be established based on the user having already logged into windows xp?

p.s I do not want to use this as it is for a user which has a login in the sql server.
"Server=SVR07;Database=servername;User ID=TestUsers;Password=12345678"


Thanks

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