New
#11
Use free Dyndns.org service to get a permanent host name for each computer involved that will always be the same regardless of ip changes. Run an update client on each machine and set it to boot with Windows. Don't worry. It's very light on resources.
DynDNS.com - Support -- Update Clients: Downloads for update clients, DDNS routers, DDNS hardware clients
Now map drives or shares from your machine(s) to his machine(s) as normal, using the host name address you've chosen. He could do the same to yours.
i.e. Your roommate computer one was made into abc.dyndns.org
From one of your computers or both, map to
\\abc.dyndns.org\sharename
Of course, sharing settings and permissions in Windows and routers must be setup correctly too on all machines. Port forwarding must be correct.