How to share a folder on Windows 7 PC to a Windows XP PC on different network

How do you share a folder on a a pc running Win7 to be accessed by a pc running WinXP on a outside network.

I have a folder on my Win7 pc, I would like to share this folder with my sister who lives in a different state and is running WinXP. How would I set this up with good security?

To share the folder on the Windows 7 pc and Windows XP from another network you have to go with the "net2ftp" which is a web based ftp client for sharing the document between two or more computer. But this is temporary solution for the same. I will not recommend you to share the important file with the net2ftp. Also if you want you can go with the TeamViewer which is another application that will allow the access to your PC from any network.