Exporting a slice as PNG

[stuffi...@gmail.com]

I've just started using CS4 a few days ago, and generally I'm very
impressed. Certainly a big improvement over using Photoshop for Web
design purposes. One thing has been bugging me though:

For a PNG-based program, I was a bit surprised to find that PNG is not
a default option for exporting a slice. I finally figured out that I
could manually change a slice to PNG using the Optimize panel.
However, it would be nice to add my PNG settings to the "default
export options" I can choose under Properties. I feel like there must
be a way to edit the defaults and/or create and save my own export
savings, but for the life of me I can't figure it out.

Also, when exporting as a 24 or 32 bit PNG, the transparency options
disappear (no pun intended!). Maybe there's something I don't
understand about the format -- like transparency is always supported
in 24 bit? or never supported? -- but I would still like to be able to
choose alpha transparency and set the matte color. I tried exporting a
slice with a translucent background in 24 bit, and it didn't work. As
an 8-bit png, alpha transparency works correctly.

One final bonus question: speaking of matte colors, I notice that if I
put a black box behind a "foreground" slice and export the slice as a
PNG, it renders the foreground stuff to display correctly on a black
background (as if I had chosen a black matte). I found the template
file where I originally discovered this behavior, and the slice
appears to be set to 8-bit PNG with index transparency and, oddly, a
WHITE matte. When trying to manually replicate this behavior, I got a
similar effect by placing a black box (a polygon) behind the
transparent bits. However, when I added other colored boxes and made
only the one I wanted visible, it didn't work -- it rendered the color
as a solid background. I may be mistaken here, but Fireworks seems to
be automatically seeing a large solid-color area behind a slice and
some objects as a "background" and blending transparent objects over
it accordingly. Is this true, and if so, is there any way to fine-tune
how it decides what the "background" is? It seems like a better system
would be setting the matte color manually, but several template PNGs
I've seen seem to use this technique instead.

Thanks.

PS I'm new to this forum so I apologize if you guys prefer a one-
specific-question-per post format. I do assume that anyone who can
answer one of the above questions can probably answer them all at the
same time.