It's Activisions problem now. They put those old sierra titles on steam. I am very thankful to finally get to play them since I didn't own them before. (Kings Quest & Space Quest) but not even upgrading DOS-Box made them playable for me.
I have to use ScummVM to even run them which somewhat destroys one of the mainadvantages of a steam-purchase (recorded playtime/seeing how long you played a game)