They're disk images, so you need to mount them. Probably easiset to do with the one in the isolinux directory, since it's already in one piece. gunzip it and mount it (as root) with
mount initrd.img /mnt/floppy -oloop
(of course you can mount it anywhere you want).
A general tip: file is your friend.
I once wrote a graphical install and package managing system for slack in tcl/tk. Thanks to the simple package format it wasn't too hard, but it sucked anyway, so I've since thrown it away. Hope you have better luck!