Hello Therapist,
Welcome to the forums.
WM will auto complete the last 29 addresses you have sent emails to. If you have the addresses in your contacts folder, it should auto complete from there. It may however wait until you hit the send button to do so if you haven't installed SP1. You can use just a first or last name and if there is only one possibility it will send(go to outbox). If more than one possibility it will give a list to choose from. It will not look these up until you click (or tab to) somewhere besides the line you are entering the addresses in.
Hope this helps.
Gary