There are a number of approaches you could try. I don't think you can get floppy images for debian sarge
any more, it's all done by CD/DVD or over the network.
But one way would be to install an old woody
version instead. The hppa files are here, you'll need root.bin and 32/images-1.44/rescue.bin:
Then if you got that running and connected to the network you could update to sarge
Or, you could try to install it over the network from an image on another machine -- here are some instructions for TFTP booting:
Lastly, there's a way of doing it using your existing HP/UX system. Basically, you repartition the disk to provide some space for the new OS, then install debootstrap
in there and use it to build the debian system:
Sounds like an adventure whichever way you go about it!