well, after hours of tinkering with the keyboard, it finally seems that the wires are the real problem. sometimes the function keys work, sometimes they don't. so i'll have to cut a bit off the end of the wires, and use some sandpaper or a knife to connect the metal part to the connectors.
the 5300 keyboard doesn't work either: one of the wires has to be inserted upside down and even then it does nothing.
@beachycove: i'll read this in the near future, thanks, but i think you fail to see the point. you see, i have no other mac with a printer port, or in fact any of these old connectors (lpt, scsi, you name it). i only have a g5, a quicksilver g4, and a first gen imac. and they all have only ethernet. the powerbook 5300 i have is only for parts, since its display is broken, and i guess there's a serious motherboard problem too, 'cause no matter what i do, it won't even get to the startup chime. belive me, if i'd have another mac with a printer port, i wouldn't even bother taking the duo apart, since i'm not an expert in hardware.