Ok,
I found that Scope_identity is working only on SQL 2000 (I'm in 7.0)
What i'm using is the following query :
INSERT INTO tbl_cases (equipment_id, date_created, status, other_problem, owner, case_school, username, password, case_user_id)
SELECT
'$session_id_equipment',
'$now_date',
'1',
'$form_problem_description',
'$session_people_id_no',
'$session_assigned_school_id',
'$form_username',
'$form_password',
'$session_id_users'
SELECT @@IDENTITY AS 'case_ident'
I tried it and it works. But I don't know if it's reliable.