I heard about this game today. It's being made by Square Enix and kind of looks to me like Final Fantasy meets Wing Commander...which are my favorite two game series so I'm really looking forward to this.
Square started developing games in the early 80s. Sierra was just the American publisher for Silpheed... it was developed by a company called Game Arts in Japan. Sierra bought and localized several popular Japanese games for release in the US... the other big one was the Thexder series, which *was* developed by Square.
Square was founded in 1983 as a studio belonging to another company. It became a separate corporation in 1986, but developed and released several games before that (which were published under the Square name).