You can change *.c and *.h Explorer icons to point your own resource dll with this small project.
This one change only c_auto_file\DefaultIcon and h_auto_file\DefaultIcon values.
Copy CFileTypeRes.dll and CFileType.exe to proper folder and run CFileType.exe with option /R or /U to change register values.
If you found errors, you may create better version and please publish it.
EDIT: For WindowsXP only ?
New version in CFileType_WS_1.zip