No Demo and DLC planned for Dark Souls
Hidetaka Miyazaki, Director Dark Souls, has confirmed that the game will have a total of 60 hours of playtime, in comparision to Demon's souls that lasted around 30 to 40 hours.
In an interview to 4Gamer Hidetaka Miyazaki confirmed the gameplay time. He also commented that there won't be a demo for the game, since he's 'not that great at making demos' and 'the appeal of Dark Souls can't be conveyed in a short play experience'.
It was also revealed that currently no DLC is planned for the game, however if in future DLC were to happen, they won't charge a penny for it.