The drivers is re-claim from Win XP inf directory. But it also work properly with W2K.
I suggest you to use the HP Precise Scan 2.02 from HP.com or below link (h20015.www2.hp.com/en/softwareDownloadIndex.jhtml?reg=&cc=&softitem=sj662ei&prodId=hpscanjet59305&lc=en&sw_lang=en) for your 5100C scanner.
Expand the file and prompt to the directory when needed ! Hope your could work too !