I'm hardly an expert on Outlook, Sharon- I don't use it because of some of the real problems with it mentioned in the several "Virus" threads(Take a look at Eudora if you get a chance- there's a version you can get for free) but you should be able to set up separate Folders and /or Groups in Outlook by clicking the "New" button then "Folder" or "Group"& then send multiple mailings only to those addresses saved in a particular group or folder.
There's folks better acquainted with Microsoft products that I that will probably jump in here to help. Good Luck!

Best, Greg