I don't have that much experience in networking over the internet. But there are a couple of things you can explore. As long as you have good security on each pc and a safe service for the network you will be fine.FTP:
The simplest option if you want to just share files. Just get some space and upload your folders.
Pros: Access files anytime, anywhere even when your PCs are off.
Cons: To modify a file you must download it, modify and upload it again.Search HereVNC:
This is a remote PC to PC connection over the internet. You can see the other PCs desktop and work just like you were sitting at it. VNC services hereVPN:
I have never use a VPN and I'm not to sure how they work, but its worth suggesting!
One Service I have just remebered relevant to FTP is www.box.net
a great free service for internet file sharing they have added many new features since I last used it - so got check it out!
Hope that helps!