IMPORTANT.... If you create a new database from the command line, or you 
clone an existing database, you can open it in an instance not specifically 
for it. But, if you want to create an instance that runs seperate from an 
existing one, you must use ORADIM from the command line to create it. 
Here is the syntax:

C:\>oradim -NEW -SID fastdb -INTPWD manager -STARTMODE auto -PFILE "c:\oracle\admin\fastdb\pfile\init.ora"

Oradim can be used to CREATE, START, STOP, MODIFY, DELETE an instance.