Quick question: Parallel or USB connections?
If it's USB, that'll explain the swap from LPT1 to the DOT4 port.
If it's parallel, then we've got a small problem, where the DOT4 port is trying to commandeer the printer and may require a full scrub out to get a bad registry entry out.
Most HP software packages have a less-than-visible uninstaller on the disk itself. I don't have a folder list available for each disk, but *usually* the file is named one of the following:
SETUP.MSI (The one in the setup folder on the disk will uninstall previous software if it's found)
You'll probably need to search for it, though here's a list of common folder locations for the (better) HP uninstaller: