each database instance uses one and only one parameter file when starting up.

Depending upon in what mode you want to run the database (DSS, OLTP or a mix) you can create many different copies of this parameter file and make necessary changes in there.

Then you can start the instance by a command like following --

STARTUP PFILE=c:\oracle\ora81\init.newsdb.ora003

(or choose whatever init file you want to start te instance with)

Sambavan is right in that in most cases the init file looks like initSIDName.ora but it could be any name as long as your OS supports that naming convetion. In Windows you can use a init file like "init.newsdb.ora003" without any problem

- Rajeev