"I can't seem to get the installer to skip or install Direct X 9.0c."
That is just telling us what ISN'T happening. To help, we need to know what IS happening. Do you get some error? Does the install just halt? And exactly where in the process of install does it happen?
What version of DirectX do you have installed? Last time I looked, MS had DirectX 10 available as the "current" version available to DL. If you have DirectX 9, then there's no harm in just letting the installer run it's course. It won't change anything if you really do have the right version installed. It will only update what is needed. I have no experience with version 10 though, and I don't know if Decal will work with it.
You can find out what version you have installed by doing the following:
Click on Start -> Run and type DXDIAG in the box and hit OK.
The last item in the list that comes up will be your DirectX version.
-----signature-----
AC - Jothony of Eastham, Chen Jo, Jothany
Vanguard - Jikar
All Retired