Just installed this driver on a Windows 8.1 system for the first time myself and it worked fine. One thing you will need to do is to turn off the verify driver checking or you will get a HASH error.
The procedure for doing this can be found here…
Note too that you may have to turn off SecureBoot in your system BIOS to carry out the steps detail above. This can be done by following the steps detailed at…
Once these are done you should install the driver in the normal manner using ‘have disk’.
I’m re-posting and updating this post as the old one had become very long see https://litespc.wordpress.com/2011/03/04/windows-7-64-bit-driver-for-hp-designjet-450c/
In short there is an un-official 64 bit driver for older HP Designjet Plotters written by jdm13.
It can be downloaded from …
I have just tested this download link (16:40 GMT 16/9/13) and it is still working.
The driver installs using the standard Windows driver update process but if you have problems search the original posting for solutions.