LAN speed varies

Hello All,

I have a laptop with Windows XP professional. My friend has a laptop
with Home Edition. Whenever we try to copy files by connecting both
our laptops via router/crossover cable we run into varying network
speeds. First time the network utilization is 4% of 100 Mbps. If we
both shutdown and restart the computer then the network utilization
increases to 50 to 80% of the link speed. Can anyone think of a reason
why that would happen? Can anyone suggest anything to overcome this
first time slowness?

Thanks

Senthil