as suggested is probably the way to go here.
But, if you can share a Mac drive with a Windows machine via firewire, which you say you can do, why do you need to do it the other way around?
Surely there does not have to be "the other way around"?
If a Windows box is connected to the Mac disk, then isn't the Mac disk, by virtue of the Firewire connection, already connected to the Windows box?
Instead of pulling the data from the Mac disk, push the data to the Mac disk.
When you have an ethernet connection, the better option, between the two machines, there is no need to log onto each machine to exchange data. Push to one, pull from the other.
P