PC release of Assassin's Creed will be somewhat of a Director's Cut, with new, exclusive side missions added. 

Press release :

London, UK – February 6, 2008 – Today Ubisoft, one of the world’s largest video game publishers, unveiled Assassin’s Creed™ for PC will be available at retailers end of March.

Following in the wake of the critically acclaimed and worldwide console hit Assassin’s Creed, the PC version entitled “Assassin’s Creed™, Director’s cut edition” will feature four brand new exclusive types of investigations, thus providing even more ways for players to explore the various locations of the Third Crusade.

Players will assume the role of the main character, Altair, and will work to stop hostilities by suppressing both sides of the conflict and experience the art of a master assassin. With more than 5 million units of the console versions sold to date worldwide since its mid-November 2007 launch, Assassin’s Creed PC is set to expand upon this success.

“We are thrilled to bring Assassin’s Creed to an eager PC audience and we anticipate the game will resonate with them just has it has across the other platforms,” said John Parkes, EMEA Marketing Director at Ubisoft. “Assassin’s Creed is a game that must be experienced firsthand to fully understand how dynamic and meaningful this title has become for video game fans worldwide.”

Source