badjim: Most walkthroughs tell you to get the ankh, the snowman and the shard/broach before entering Dons' dark room. This is the easiest way to beat chapter 7 but it skips the scalp/wig sequence.Instead do this:

1) Start chapter 7 and go straight into Don's dark room. Use the drain cleaner on him to get out.
2) Run upstairs into the nursery and pick up the shard. Stab Don with it to escape.
3) Go back to Don's dark room and grab the book. Use the hammer on Don to escape.
4) Go upstairs and use the secret passage. On the first elevator down, Don will try winching pulling you back up but you can just jump off.
5) Go to the crypt. Pick up the ankh. There is a sculpture on a pillar near the entrance, push it and it will land on Don's head.
6) Head for the theater. You will see the Don wearing Harriet's scalp as a wig, and will then find Harriet's body.
7) Head for the make up room and grab the snowman from the jacket. You can finish the rest of the game with regular walkthroughs.

You may find this helpful:
https://www.youtube.com/watch?v=SAw6BpZLMuU