Win2k drivers use a different scanner software that is rather specific to the Deskjet F4580. I searched and could not dissect the software package for this printer but I will tell you the most common scanner software for Windows 2000 was called HP Director. That is the missing element and if it did not load with the 990c driver, I warn you to be suspicious of downloads offering that program but I do not have it. It's incorporated in the printer's Full Feature drivers.
It is possible the old TWAIN-SCSI could have interefered with the installation of HP Director during the Deskjet 990c installation but not likely. I recommend trying scanner programs associated with WIA. Perhaps your Windows 2000 has Paint or a Camera Scanner Wizard you could try.
Try searching the PC for HP Director on the Win2k system or using a Windows program to communicate. That is going to be the only way to scan. There is no real "driver" used to do that. Scanning is function of the software. Let me know if this helps you any. I hope so.