cdosys.dll missing on Set Screen

i just reformated my pc's hdd using the windows 2000 pro
cd that came with my pc and it was installing the windows
files and i got a Alert, that said i was missing the file
called cdosys.dll, it said i could ingore,check cd-rom or
stop setup, i choosed ingore and it went on with the
installation. i wanted to know how big of a program is
this and if i could get that dll file from somewhere and
it would work. plz help thnx