This needs to be filled in...mainly, thanks to this page (and what a neat-looking project, BTW), I've figured out how to get Debian aware of the new package:
cp your_package.deb /path/to/mirror/dists/pool/main/y dpkg-scanpackages /path/to/mirror /path/to/overrides | gzip > Packages.gz
(Takes about half an hour on a 2GHz P4.)
And where do you get dpkg-scanpackages? From dpkg-dev, of course.