Here's what one of the people on our team suggests:
1) Make sure a supported version of DirectX is installed.
2) Make sure no other programs are running.
They can check their DxDiag for the version of DirectX that's installed. (It would be helpful to have a copy of their DxDiag).
"To find out what hardware you have on your PC, open the DirectX Diagnostic
1. From Windows, click Start->Run
2. In the Open: box, Type DXDIAG and click OK
The DirectX Diagnostic Tool will display all of the relevant hardware and software on your PC."
After you run DxDiag, could you click Save All Information and send the file to me at emily -at- telltalegames.com?