For some devices U need just to run MAKEDEV (scrip from /dev/), but that are just devices, like serial, apralel ports, scsi adapters, but no direct hardware devices. For them you usually need module in kernel. EG if U want to mount windows hardrive, you need /dev/hdxx device and also vfat support in kernel. And probably support for yoour hardrive, if it's not a standart one.
Try to download som linux kernel sources and browse the Documentation directory.
bubak