Power Partner User:

To bulk load Partner user in salesforce below are the steps:

1. Create those Partner Users as Contact.
2. But to create contact we should create account first.
3. Create account and enable this account as partner account.
4. Load all contact under the account created in step 3 with ispartner=TRUE
5. Now create 1 user with correct account and contact id populated
6. step 5 will create partner role now update users role with appropriate role ids
7. create bulk users same way we created in step 5