I'm not sure if by folder you mean the AUM zip you've already downloaded. If you do mean that folder,you'll also need the resource zip.
Expand "Resources" in the chm file table of contents and you will see the link which is:

http://aum.conitec.net/aum82code.zip


Translation from German to English from google:


http://translate.google.com/

Hello!
I have just downloaded 82 AUM. It's the English version. It describes how to create a 2D game programm.

Unfortunately, this file, 2dspace1.c, is not in the folder which I've downloaded. Where can I get this file?

Thank you very much