Couple of things about DW:
1. I have written extensions for it, it's not easy. You can write them in MacroMedia's flavor of JavaScript or in C, which requires Visual Studio. The extension we wrote was for back when we were still on Apache and wanted to see the contents of our included .shtml's inline in the file that was being edited. They have fairly decent documentation on how to build extensions on their website.
2. If you are using DW to edit .adp files make sure you set DW to NOT "fix" HTML code that doesn't look right to it. Edit->Preferences->Code Rewriting is where that stuff is. Otherwise DW will mess up the templating system tags.
