Dunno what to tell you. In Office 2010 if you want to just type letters and have it jump to a sender you have to have it arranged by From.

The other thing you could do is click in the Search box and start typing the name there. It would then dynamically filter the list to show you matching messages. Not quite as accurate, since it won't automatically be limited to From (though you could click "From:" on the Search Tools group) but it'll work.