I bought this book and have to say it's perfect for beginners and intermediates. It fills in a lot of gaps if your self taught. I swear I browsed through the book the day I got it and immediately found something I had been trying to figure out and went right to it.
Not only does it give you step by step instructions for certain tasks but if your like me it spawned a lot of ideas.
There are many books starting to pop up now about WSS. I purchased a few that turned out to be a bit above my skill level right now but this one is just right. Trust me, if you want a big jump start in expanding your SharePoint Designer experience, this book will do it. Microsoft Press
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