In the window where you create your task or calendar item, there is an
option for a reminder. Look for the little bell or alarm icon. Then
select from the drop down list when you want the reminder to pop up --
anywhere from 5 minutes before appointment to 1 month.
In my opinion, Outlook is not as well suited to this as one of the many free
alarm clock or reminder programs available on the Internet. Start at http://www.pricelessware.org/