If you wonder what minimum permissions you need to use SqlDependency with SQL Server 2005 then look no further. This code project article definitely works and is the most complete one I've found. Note that setting minimum database permissions for notification isn't exactly the easiest task on the planet. Actually through experimenting I've managed to create a service_queue in sys.objects that I couldn't remove without restoring the database entirely (luckily I am using RedGate's SQL Backup 5 for backing up my databases - it makes the backup and restore process so easy, not to mention the encryption and compression capabilities).
Anyway, after restoring the database to the initial non-notification enabled point (clean state), I managed to apply proper minimum permissions following the mentioned article.