Hi there,
I do the following when I want to do a fresh re-install (NB: I use MySQL – your database may differ):
1. Log onto MySQL.
2. Delete the 'alfresco' schema.
3. Recreate the 'alfresco' schema.
4. Grant the 'alfresco' user all privileges over the 'alfresco' schema.
Once you do this, Alfresco will re-create the tables, etc. on start-up.
I haven't tried this, but the following should work as well:
1. Run '<alfresco_home>/extras/databases/mysql/db_remove.bat'.
2. Run '<alfresco_home>/extras/databases/mysql/db_setup.bat'.
Hope this helps.
Darryl