1. So I need a file server in addition to WinSCP right?
Lets say I have 2 windows PC's A and B.
2. I like to send a file from A to B. On whitch PC must I have WinSCP and HSS server?
3. What if file transfer is both ways?
You need to have a server on the other machine than the one you are sitting next to. No matter what the direction is.
4. Lets say I want to reed an XML file on both computers. Any of the computers can update the XML file. Can I synchronize this files due to an update on any of the files? Can this be done on an time interval as well?
Both is possible. For update on change, see keepuptodate command