Well I did get it to work on my 2000 Pro machine.
I found my Designjet 430 disk and ran it during the Add a Printer WIzard and it had the driver on it to make the 750 work.
I have no clue as to why it couldn't find the driver already installed without having a disk.
Something else I had to do: It installed the first time as an E size printer which it is. To get it to recognize the D size paper I had to go back and install it also as 750 D to recognize the 24 inch roll and the 750 not say the media was to small when trying to plot with a 24 inch roll on it.