set ORACLE_SID=tammy

created the service with oradim (WIN)

C:\>oradim -new -sid %ORACLE_SID% -intpwd MYSECRETPASSWORD -startmode M
Instance created.

create the folder tammy in the following directory

C:\oracle\product\10.2.0\oradata\tammy

created init.ora in the following directory 

C:\oracle\product\10.2.0\db_1\database

inittammy.ora

control_files = (c:\oracle\product\10.2.0\oradata\tammy\control01.ora,
                 c:\oracle\product\10.2.0\oradata\tammy\control02.ora,
                 c:\oracle\product\10.2.0\oradata\tammy\control03.ora)

undo_management = auto
db_name = tammy
db_block_size = 8192

Start The Instance

SQL> startup nomount
ORACLE instance started.

Total System Global Area  113246208 bytes
Fixed Size                  1247588 bytes
Variable Size              58721948 bytes
Database Buffers           50331648 bytes
Redo Buffers                2945024 bytes

Create The Database

create database tammy
  logfile group 1 ('c:\oracle\product\10.2.0\oradata\tammy\redo1.log') size 10M,
          group 2 ('c:\oracle\product\10.2.0\oradata\tammy\redo2.log') size 10M,
          group 3 ('c:\oracle\product\10.2.0\oradata\tammy\redo3.log') size 10M
character set WE8ISO8859P1
national character set utf8
datafile 'c:\oracle\product\10.2.0\oradata\tammy\system.dbf'
         size 50M
         autoextend on
         next 10M maxsize unlimited
sysaux datafile 'c:\oracle\product\10.2.0\oradata\tammy\sysaux.dbf'
         size 10M
         autoextend on
         next 10M
         maxsize unlimited
undo tablespace undo
         datafile 'c:\oracle\product\10.2.0\oradata\tammy\undo.dbf'
         size 10M
default temporary tablespace temp
         tempfile 'c:\oracle\product\10.2.0\oradata\tammy\temp.dbf'
         size 10M;

Run Scripts
SQL> @?/rdbms/admin/catalog.sql
SQL> @?/rdbms/admin/catproc.sql