SharePoint 2007 does not come with the ability to add reminders to calendar events. If you want to have a reminder for one-time or recurring event you will have to get creative, write a timer service, or buy a third party product. Here are options for all three:
You can use a task schedular outside of SharePoint and provide a link in the reminder email that leads them back to a SharePoint site or list. The link can also pre-fill a NewForm using a little jQuery.
Timer Service Approach
You can create a custom timer to evaluate a calendar and send reminders for all events due on that day. Here is an article on how to do that: http://msdn.microsoft.com/en-us/library/cc406686.aspx
Third Pary Approach
The leader in this area seems to be a product called Pentalogic Reminder. It can be pricey but if it will do everything you are needing to do except create a new item in an existing task list. It will only send emails. http://www.pentalogic.net/sharepoint-products/reminder