Network performances

I have a server with SuSE8.1 I have noticed that Linux PCs with old kernel 2.0.x have bad network performance. (92 secs for a PC with 2.0.x against 7 secs for a PC with 2.4.x to copy a 36MB file - same HW) Does anybody have some hints, other than upgrade to newer kernel, since not always possible? Thanks