ummm. Never used mssql, but youldn't you have to make the 2 server instances listen on different ports?
I was able to connect on different ports for the two SQL servers.
Database connectivity specific to TCP/IP and Port. Sql server default port is 1433; second instance sqlserver(ex. msde netsdk instance port will be 1663 - you can get the port value from entreprise manager instance properties)
so url config will be as follows...
For an information..
MDAC 2.6 and later can automatically idetntify the ports of two instance by name. for that configuration will be like DBSERVERNAME\INSTANCENAME (localhost\NetSDK - above).
In a final word sqlserver jdbc requires tcp/ip and port for connection. you can replace ip address with servername(ie. wins name) or alias value(from host file).