Task Manager Help.

It appears that double-clicking the grey parts of the Task Manager window triggers this. (Not the edge, and not the white parts where all the things are listed.

So just double-click the grey areas around the list to get your Task Manager menus back. (Bare in mind that I'm using XP, so I don't know if this is different for Vista.)

It works the same in Vista.

Like Judgment said, just double click the thing and it'll go back to normal.