Found these SharePoint Designer 2007 demos from Mike Gannotti’s blog. There are six video demos along with articles on using various features of SharePoint Designer such as Creating Page Layouts, workflows and basic UI Customiazations. If you are trying to wrap your head around where and when (and how) you should use SharePoint DEsigner, these might be a good starting point.
Now that we are done our book (WaaaaHooooooo), I am hoping to get some more of this type of content created so I can post here and not be such a terrible blogger. Especially related to some of the applications I have been neglecting lately including InfoPath, SharePoint Designer and Project Server and how they integrate with WSS & MOSS.