I don't use PDT, so can't really help you. If no one else here can, you could try searching the eclipse.tools.pdt newsgroup.
As far as an IDE being defined by code completion and function list features (which I sometimes find irritating anyway), I wouldn't go that far. But if you can't get it figured out for Ecliplse/PDT, there are a number of other options, such as Aptana Studio (also Eclipse based and what I currently use), PHPDesigner (not open source but not too expensive, though on 2nd thought I think that's Windows only), and assorted other editors/IDEs you can read about in the "Echo Lounge" forum here with a little searching.