If you know the syntax, here are the steps.
1)Create database with system datafile of sufficient space.
2)Create USERS,TEMP,RBS tablespaces and Public Rollback Segements and run catalog.sql, catproc.sql. ALter system user defaulted to users and temp tablespaces.
3) run the rest of the scripts CAT*.sql, DBMS*.sql, UTIL*.sql depending up on the options you wanted on the databse.
4) Create DATA and INDEX tablespaces for your data per requirement.
Do you have currently database running or not. Even if you don't have there should be sample init.ora file where you have all the required(manadatory) parameters. Make a copy of that parameter file (say your database is PROD) to initPROD.ora and edit the database name and control files names which reflect the database you are gonna create and create database.
Not sure. you have dbassist or not on Personal Oracle. If its there it should be in your programs or serach for binaries in ORACLE_HOME using windows search facility.
If you do have your its lot easier.... to create database.