I have a couple of problems with my copy of

I have a bunch of questions, and appreciate any help or advice.

1) I can login to the SQL*PLUS and attach to the DB, but I
am having problems with the DBA STUDIO locking up. It sez JREW.EXE not responding when I shut down my system.

2) I have installed the DB, created a DB, but haven't set the parameters in the .ORA file. Is this a problem? Also, I have two other DB instances that the install picked up from some prior install. I went into the ADMIN for WIN console and found the service on for these DB's, but I can't seem to delete them. Any help or suggestions appreciated.

3) I have logged in as internal/oracle as sysdba, but I don't show up as a user. Am I still setting things up? Because when I open the DB it shows my settings, but I can't open tables or view schema. Have I finishe the create table\tablespace?