are you using sqlserver 2000 or 2005? connection varies for them, see the coed below. Get appropriate driver from microsoft site.
String connectionstring="jdbc:microsoft:sqlserver://nishanths:1433";
username="abc";
password="abcd";
//use any one of the line according to your sqlserver version
//DriverManager.registerDriver(new com.microsoft.sqlserver.jdbc.SQLServerDriver()); //Use For SQL Server 2005
DriverManager.registerDriver(new com.microsoft.jdbc.sqlserver.SQLServerDriver()); //Use For SQL Server 2000
Con = DriverManager.getConnection(connectionstring,username,password);
Thanks,
Nishanth.S