A user had a question about Outlook 2007 and 2010's ability to fire reminders from every calendar:
How do I turn off the reminders from other calendars? I keep several calendar folders in my profile and only want reminders from my default calendar. At the end of each year, I copy the old pst file to use as an archive. Now I'm getting two reminders for everything. What setting in Outlook will referee which calendars actually get to generate a reminder?
You can disable reminders in pst files that are not used as a delivery location for an email account, but it will affect all reminders and flags, not just calendar reminders.
Just above the folder size button is an option to "Display reminders and tasks form this folder in the To-Do Bar". With the enabled, you'll get reminders, with it disabled you will not get reminders and tasks or flagged messages will not show up in the To-do Bar.
If you don't see the option, the data file is used as a delivery location for an account or is the default data file.
If you need to keep the flagged items in the To-Do Bar and only want to get rid of the calendar reminders, create custom list view that groups by reminders then drag from the RemindBeforeHand:Yes group to the RemindBeforeHand:No group to turn them all off. We have a tutorial at Change reminders on several items.
Reminders in secondary calendar
We also receive complaints about this feature from users who were in the habit of creating appointments in a secondary calendar folder to use as a journal. These appointments are always in the past and now they always trigger a reminder unless the user remembers to deselect the reminder.
Unfortunately, unless the calendar is in a different data file, you won't be able to disable the reminders using options within Outlook. You can use VBA to not set reminders on events in specific folders. See How to Remove or Change the Reminder on All Day Events for the basic code.
You'll need to set the reminder to none when you create the appointments. You can also turn off default reminders in File, Options, Calendar and set them only on appointments that need to have reminders.