I'm not too familiar with dreamweaver, but give this a try (I don't have PS in front of me, so this is from memory, so I might miss a step or two.):

When you setup your text in photoshop on a transparent background, Save For Web (Ctrl + Alt + Shift + S).  This will open up a new window showing how your image will look saved for the web with different compressions/colour tables.  Select to save it as a GIF and then make sure that the transparent option is checked.  Then tweak the number of colours in the colour table until you have a nice balance between file size and image quality.  Hit save and then pop it into Dreamweaver.

Since we're using me as an example, my avatar is a transparent (and animated) GIF.  It'll look good on most light coloured backgrounds.  The thing with transparency (and what harmspen was alluding to) is that you have to decide if they are going to go on a light or dark background and then matte them properly.  You'll notice a matte option somewhere near the transparency check box.   Pick a colour that's close to what you think the "average" background colour for your image is going to be.