I finally got around to adding some of what I've discovered over the past few weeks to the NODOWS phing build files. Its a very good thing.
I've figured out a quick and easy way to glean download targets for the packages, and I think there must be a way to calculate dependencies, but I'm not too crazy about worrying about that for now. Phing makes it easy enough to maintain a complex set of tasks so I think I'll just manage the dependencies manually for now.
I have to say I am a little stumped on how to handle the disk images, partitions, and filesystems with phing. In the FreeBSD builder, the mdconfig, bsdlabel, and newfs tools are used. The GNU tools I'm familiar with are fdisk and mkfs.ext2, but they require interactive input from the user, which doesn't fit too well into a build script. One possibility is to create a partition map manually, save it and use it over and over again. Not very elegant though, but perhaps practical.
http://wiki.xensource.com/xenwiki/InstallGuestImage
APT?
I actually just figured out its not too too difficult and unwieldy to install apt, and that could make more complex build configurations a lot easier. Furthermore, once the build configuration is complete, apt and its sole dependencies (such as gnupg and friends, though many of the depends packages are also used by Apache2) can be removed via dpkg freeing up to 40 or 50MB.