I'm using dreamweaver as IDE for coding PHP and use inc files for some Drupal modules. By default Deamweaver does not highlight inc files but can be made to highlight syntax for such files. I also did the same for Drupal module extention. Module files are PHP but use the file extension .module, which Dreamweaver does not recognize as PHP code, so we'll register the .module and .inc file extensions as the PHP document type.
To do this:
Open c:\Program Files\Macromedia\Dreamweaver\Configuration\DocumentTypes\MMDocumentTypes.xml
Look for winfileextension="php,php3" or macfileextension="php,php3" if you're on a mac and simply add inc and module to the list:
winfileextension="php,php3,module,inc"
Save it, and restart Dreamweaver and you should be good to go.
For more info see:
http://kb.adobe.com/selfservice/viewContent.do?externalId=tn_16410&slice...