Hi,

I dont know the restriction of the number of instances you can have ( i have worked with 4 instances in 1 machine).

Regarding the control file ,you have to copy the init.ora file change the parameters as required( like database name ,location where the control files has to be created etc)

Then at the command prompt set the Oracle Sid to be pointing to the new sid

set ORACLE_SID=new_sid

Then issue the create database command which will create the controlfile for the new instance and also the req system and other datafies..

-Anand