@richlex
Hello,
The Directx SDK is actually for programming directx using C/C++ . If your son really gets into programming it would be most useful then, for now, I think you might need to install the Directx runtime, probably version 9.0c. It's good to have the latest Directx runtime installed anyway, regardless of DarkBASIC. Check out the following link:
Direct X
If after installing the DirectX 9.0c runtime you are still getting errors, you may want to check the capabilities of your graphics card and make sure all of it's drivers are up to date.
Though you mention the CLI tab I'm going to try and avoid making assumptions. Are you able to install the main programming engine (i.e. DarkBASIC itself - not Dark Matter necessarily - Dark Matter is a series of useful 3d models, pictures, music and sound - makes things easier, but it's not a necessary component) ? If you are able to install the main program, and you are ready to launch it, do so. The main screen should be black and run through a series of component checks. In the bottom left hand corner should be the version.
If it reads
DARK BASIC V1.12 ENHANCED, you're pretty much good to go. This version offers all of the functionality versions before 1.20 offer, so you can sit tight until the latest version 1.20 is available again for download. If it doesn't read ENHANCED, then there won't be available some of the more advanced commands - which should be ok since your son is just starting. Again, you'll just have to wait until 1.20 becomes available for download again.
Enjoy your day.