Network Win2000 & Win98 Problem

I have a network of a Win2000 PC(P4 2GHz) & a Win98 PC (p3 600). Both PCs have a common software program installed locally with the datafile on the Win98 PC.(This can’t be changed) The Win2000 PC runs like a dog when accessing this particular datafile on the Win98 PC. I have been told it is a networking issue. Does anyone know why and how to fix.