HAL depends on the userspace device manager udev, described in Chapter Dynamic Kernel Device Management with udev (↑Deployment Guide). Find more information about D-BUS and HAL at:
http://www.freedesktop.org/software/dbus/—D-BUS project
http://www.freedesktop.org/software/hal—HAL project
/usr/share/doc/packages/hal/spec/hal-spec.html—HAL specification
/usr/share/doc/packages/udev/—udev documentation