This will hopefully help others who have pulled out their hair trying to understand and fix this problem.
Yes, the 2400-series of printers are old, but they are built well in terms of hardware. The software side of HP is seriously lacking, however.
Whoever stumbles into this thread has probably searched through various tech articles posted online by HP, and their instructions are abysmal. They are poorly written, so understanding and following the instructions is quite a task. I'de say its up there with assembling Ikea furnature.
With that said, I ran into the same issue as the above poster: very poor USB performance. Installing the drivers was a chore as well, as these did not install as seamlessly as a modern day USB device. You'de have to click on the "Have Disk" in order to select the printer. As an IT guy who has been in the industry since the 90s, it took me a long while to remember that the older devices need to be walked through the installation process - even if they have USB capabilities.
The interesting thing is, the 2420 is designed with USB 2.0 - you would think it would have an easier time connecting and installing. Each and every time I attempted to connect and install, Windows kept finding a 1284.4 device and would only partially install as drivers are not available (although 1284 specification is for parallel and this should come with Windows). No difference, because I was connecting via USB and so the issue was, it appeared the print jobs would be routed very slowly through the DOT4 print emulator. Print speed was horrific, so I knew there was a problem that needed to be solved.
Well, my first attempt was to update the firmware. My attempt *appeared* to work when I used the executable firmware software. It took some time, the software went through the progress bar and finished with a "smiley face." I should have known better. The printer restarted with an RFU error. From there, did what others attempted to do: reflash the printer with a LPT port connection. I dug up an older PC, connected, reflashed... the printer stuck with "CYCLING POWER" but never restarted. That was the kiss of death - blank LCD screen on printer when ON. I needed to order a new Formatter Board via e-bay as once a firmware flash goes bad, its over. Installed the replacement Formatter and the unit sparked to life again.
The old firmware that gave me issues was dated 20050823 - 08.109.2
The current firmware that I downloaded and installed is dated 20120113 - 08.120.4
With new firmware, the USB port now functions at proper speed as it should. It still prints via the DOT4 port, but speed is A-OK now.
I highly advise caution to anyone who attempts to reflash these printers, do not even think of doing it via USB. It should only be done via LPT or RJ45 (network). To play it safe, just do it via LPT.