I found the solution and (as a good open source philosophy follower) here I publish my solution:
the solution was quit simple, as it was written clearly in the file "devices.txt" under /usr/src/linux-X.Y.Z/Documentation/ .
In this file you got all the possible combos of devices that can be eventually soft-linked into the devfs (/dev).
The simple IDE bus devices are listed as follows:
BUS 0 (block devices)
3 block First MFM, RLL and IDE hard disk/CD-ROM interface
0 = /dev/hda Master: whole disk (or CD-ROM)
64 = /dev/hdb Slave: whole disk (or CD-ROM)
so, to build up (for ex.) a softlink to /dev/hda mknod should look like this:
mknod [OPTION]... NAME TYPE [MAJOR MINOR]
Then chgrp it to "disks" and set the perms to 660
same thing, but with different params for devices on BUS 1 wich have 22 as MAJOR and 0 (master) and 64 (slave) as MINOR
22 block Second IDE hard disk/CD-ROM interface
0 = /dev/hdc Master: whole disk (or CD-ROM)
64 = /dev/hdd Slave: whole disk (or CD-ROM)
will bring my /dev/hdd back to life...
hope it'll help someone!