I have recently been doing a lot of database consolidation and as a result have found it necessary to create more than one SDE service on my database server.
First you must locate the directory that contains the default file location for your SDE service, on my server this is C:\ArcGIS\ArcSDE\ora10gexe from the folder name you can see that this service connects to an Oracle 10g database.
Copy the entire contents of this folder and paste it back into the same parent directory and rename the directory so it represents the new service you wish to create.
Under the new location C:\ArcGIS\ArcSDE\<newservice> locate the ect folder and edit the dbinit.sde file. This file contains the Oracle SID of the database you connect to, edit this so it connects to your new database. In the same location edit the services.sde file. This file contains the name of the new service and the port number it will use. Change the service name from esri_sde to the name of your new service and the port number to a new free port. I always tend to keep all the service ports close together.
You also need to edit the services file in C:\windows\system32\drivers\ect. Add the name of your new service and port to the end of the file.
Once the above configuration is complete open the command line and run the following sdeservice -o create -d oracle10g,<SID> -p <sde password> -i <newservice> -H <path to the new folder> once complete you will see the new service under windows services.