Sorry for the late reply – I had a problem with outgoing email from my forum and didn’t get a notification.
When using the DFFS Installer it basically adds a Content Editor Web Part on the NewForm, DispForm and EditForm that loads the DFFS files. If you have installed and DFFS Installer tells you that it is installed, but it still doesn’t work on that specific form (that you had modified in SPD) I’m afraid it is not much I can do about it.
You can check the following: Ensure the URL shows /Lists/YourList/NewForm.aspx – it must be the default NewForm.aspx that is the default form and not your copy.
Alexander