Get the SlackBuilds from dropline, and use them to build the packages on vanilla Slackware. BTW. IIRC new HAL versions do not do automounting, this is delegated to GNOME Volume Manager or KDE (3.4).
It may be useful to look at usbmount, which does of USB media with just hotplug and udev.
(They offer Debian packages, but it is a relatively simple script, so it should be no problem getting it to work on Slack.)