DOCBOOK-APPS: Creating or converting PDF images

What are people using to create PDF format images?  I've got a bunch
of screenshots as PNG files, and when I convert them to PDF with Image
Magick they come out badly, not completely unusable, but definately
worse than they started out.  If I just use the PNG files, they also
show up in the resulting book PDF with this same reduced quality.

I was thinking it might be Ghostscript installation, but I don't feel
like taking the time to rebuild it without checking to see what others
are doing first...

If you want comparison images to see the differences I'm getting,
here's an example:

http://zaius.chimpware.com/~rosss/sample.png
http://zaius.chimpware.com/~rosss/sample.pdf

Sean Ross
Corvallis, Oregon, USA