While your question is somewhat vague as to what you man by 'hosting' (website?)
I would just pick up a 4 port hub and then jack each machine into the hub
then out to the net.
|----------------LAN SIDE---------------------|----WAN SIDE|
[machine a] -> [eth0/nic] -> [4port hub] -> [DSLmodem] -> [net]
[machine b] -> [eth0/nic] ----^
as far as resources go..
Windows only.
if youre hosting a website from 'machine a' (gateway)
in your current configuration and want to share out hard drive resources or file
system(s) from machine b through it all they have to be is in the same
workgroup and each has to have a mappable shared drive. then you can map
a drive from b to a and then utilize the resources on 'machine b.'
linux is different, unix is as well. differing OSs can make this far more
complicated than this needs to be.