need help with ORACLE V6.0.27.7.1 on silicon graphics,rollback segs

[Beverly Seavey]

I am trying to add a tablespace to our database ( we have been getting
by with just SYSTEM up until now.)

I was able to create a tablespace using the stamt:

	 CREATE TABLESPACE TS_DAT_2
	 DATAFILE 'TS_FILE_2.DAT' SIZE 10M;

Then, because my understanding is that I need a non-system rollback
segment for a non-system tablespace, I tried to create a rollback
segment for my new tablespace:

	 CREATE ROLLBACK SEGMENT RBS_DAT_2
	 TABLESPACE TS_DAT_2;

ORACLE gives me the following error msg:

 ORA-01552
   cannot use system rollback segment for non-system tables.

 The SQL Error msgs manual advises : Create one or more private or
 public rollback segments, shut down, then start up again. You may need to
 modify the INIT.ORA parameter ROLLBACK_SEGMENTS_REQUIRED to acquire one 
 of the  new private rollback segments.

 This all seems circular: how can I create a rollback segment if oracle
 won't let me? The only INIT.ORA parameter that looked remotely
 relevant is DC_TABLESPACES, which has a default value of 25.

 I am using ORACLE  RDBMS V6.0.27.7.1