You can store your list wherever is appropriate for your application scenario (which you know a lot more about than we do). These are all possibilities:
1) In a property in the Outlook item
2) In the both of a separate Outlook item or a CDO hidden message
3) In a text file
4) In a database
How you access the data in the list depends, of course, on where you store it.
Any code to initialize controls goes in the Item_Open event handler for the form. Did you look at the code behind the sample form on the page I suggested?
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Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers