In this forum, I read many times questions how to build DS89C4X0 programmer - but it's question completely wrong, sourcing from absolutely lack of understanding of memory programming procedure of these chips.
Somebody just order free samples from Dallas-Maxim and even when it arrives, just don't know what to do with them and he is even lazy to read datasheets and application notes.
Because in application note, which wek pointed to, is all you need to build "programmer" for these chips. I wrote "programmer" because you even don't need programmer at all, you assemble boards with blank devices and at finishing construction you put a firmware into it through bootloader and serial port - it's purpose of bootloader.
So this construction is nothing special, just "extended" copy od picture from application note without explanation how it works.
So newbie build this "programmer", and maybe find out it's not working, because of some problem... but the main problem is laziness - read datasheet and application notes and you find everything.
Jaromir