BE,
Outlook is a bit more for the serious person...
While creating your mail account, you are providing details such as your Name etc.
If you want to change this, go to Options and Accounts and double click the mail account.
When sending mail, Outlook uses always the account set as default.
This is a bit a pain in the neck for notebook user travelling around with several accounts.
Everytime you want to change your profile you can do that by creating a new account and than set this one as the default one...