First delete the existing file then it will allow u to create the new file.
entries=5 means atmost u can give 5 users sysdba privileges.
by default it is only with internal.
to give the privilge to a user say mike
create a database use mike . the using internal
sql> grant sysdba to mike;
so next time u can log in as
sqlplus mike/ as sysdba
then u will be able to startup and shutdown database as mike also
entries=5 means other than internal any 4other users can be given sysdba privilege
regards
Amit Tandon