-E = trusted authentication (your current windows user account)
-S = Servername
OSQL -E -SSQLDB1
be aware that the osql is case sensitive
[BOL] "Running the osql Utility"
ps just for giggles i copied osql.exe into %systemroot%\system32 on a windows xp client in my home network (this client has no SQL Installation).
i then used the above command to connect to my other pc(with SQL).
works like a champ!