USB to ethernet is slow...how fix?

When I send data over my home LAN ethernet to a hard drive running on a USB
2.0 its very slow data transfer. This is PC to PC over 100baseT wired home
LAN to do disk backups. The slowness occurs in the translation from
10baseT100 to the USB 2.0 and the CPU is 100% utilized.

Are there cards that offload the CPU processing needed to do this
translation?

I have a PCI combo card (w/firewire), brand new installed.

The following clues narrow the problem down to the USB to ethernet
conversion as the problem.:

PC to PC over ethernet from installed HD to installed HD is very fast.
PC from its own C: drive to the USB 2.0 drive is very fast.
but when do PC to PC over ethernet to save data on theh USB 2.0 drive its
very very slow...like 5x slower then drive C: to USB 2.0.

Any thoughts?

Here are my thoughts,
your Lan is built in to the motherboard, correct?
Seems like your CPU has to deal with the lan, and the usb overhead.

So this is what I'd do. Make sure you have the latest drivers for your
chipset and for the PCI add in card (if any for that).

then I would move things on the lan, over to your C drive, then from
that drive to the USB, since it would be faster to do that then to send
it lan to usb.

without me sitting in front of your computer and checking everything
out, I can't tell you if it's fixable or not. probably not, unless
latest drivers help.
even a mb bios update could help.

I've done similar things myself, and going to the USB was always slower
then going to a harddrive in the computer, but i don't recall it being
5x slower for me, more like 2x as slow.