If you're getting a "D3DXCompile failed - result" error upon shooting the first enemy, this should help you fix it.
Go to http://www.microsoft.com/en-gb/download/details.aspx?id=35 and simply download and run it. It'll update your DirectX to the latest version.
It's also possible that your graphics card doesn't support shaders. No worries, though. The next update will run a check to see if you can run shaders, and if not, it won't use them. You just might miss out on some neat effects, but the game will be playable.