Well, as long as I'm asking questions, I may as well ask some more.

I'm beginning to receive interest from potential clients whom I know
nothing about. I have no idea how much knowledge they have regarding
copyright law, nor of their reputation. I'm looking for ways to protect
my work and the samples I send.  If  I send hard copy, even color
xeroxes, I risk the chance that they may scan the work and use it
without my permission.

For those of you who send samples of your portfolio on disk to potential
clients, do you use a digital watermark?  It seems that a low resolution
file is not enough to protect them from using your images without
permission, since so many applications require only low resolution
anyway. If you're not using watermarks, how do you protect your work?
Is there a standard resolution you use for showing portfolio samples,
such as approximately 400 X 600 pixels?

Thanks again