It says this in the OP, and this isn't dsixda's kitchen, but here you go :
1) drag and drop image onto unpackimg
2) change files in ramdisk
3) double-click repackimg
As you can see.. laughably simple. The zImage is the compiled kernel source, there are no files to get out of it. The only thing you change is the ramdisk.
I just dragged my boot.img and dropped at unpackimg.bat
and i get two folders
1) Ramdisk
2) split_img
but Ramdisk folder is empty
and there are some files in split_img as i attached the snapshot