why is 98 so much faster than win2k?

Yesterday I discovered that my 98 box could pull a 300+mb file off of my nt4 sp6 server in about 8 minutes. My Win2k box dell 1Ghz and my XP box Dell 1.5 ghz both take about 150 minutes. All three are running off the same switch. I went to another area of our facilty and tried downloading the same file on to another dell (same model) running W2k, same results. On a NT4 ws connected to the same subnet, same switch, it took 30 minutes. The 98 box has an intel pro 10+ nic, the dells all have 3com 3c905c. I tried different settings on the 3coms (auto select, 100mb full etc), I downloaded the new nic driver from dell dated 10-2001, all with no effect. Anyone ran into this before?