Don't waste your money on Dreamweaver unless you need the advanced site management functionality of want WYSIWYG designing (which it sounds like you don't, if you're writing PHP). If you do go with Dreamweaver, or if you already have it, don't bother with any commercial add-ons. You don't need them, especially if you're just learning.
The best online resource for learning PHP is the manual. It's got pretty much everything you need. Aside from that, I'd recommend picking up a copy of O'Reilly's Programming PHP. It was written by the creator of the language, so it's about as good a reference as you're going to get. You can probably find a copy cheap on Amazon or Ebay.
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