Yes! Type the person’s Yahoo! or Windows Live ID, and from the pull-down that appears below the text box, click Instant Message (their name).

An instant message window appears. Click the Plus icon at the top of the conversation window to add the person to your Messenger List.

Click the "Next" button.

Select the group and identity for the new addition. If you want, you can also include a brief message along with the request.

Click the "Finish" button.

Here’s the best way to edit contact info for people on your Messenger List:

Right-click on the individual in your Messenger List and select "Contact Details."

Enter or edit the information and click the "Save & Close" button.