I'm with Nate. Assuming that your DSL modem is a NAT Router/Firewall
type device, things should be fine. In your internal network you then
don't have to worry too much about security, unless you're going to
let strangers wander in and plug their device into your switch. This
is the simple solution you're looking for.

scp/sftp will only need minimal setup and is always a good way to go.
I once played with snfs, but that's a bit more complicated.

If both machines will be getting a public IP address, you'll want to
be running some sort of firewall on both machines. As they would both
be on the Internet, you would want to stick with secure protocols like
ssh/sftp/scp, or establish a VPN between your computers. (Open VPN or
Hamachi would do the trick http://www.hamachi.cc/). Going down this
route however would not be the simple solution that you're looking
for.

--
Andrew S. Zbikowski | http://andy.zibnet.us
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