[ILUG] File syncing

[Dj]

Hi,
I've a requirement that someone might have some tips on.  I have a file 
server with users from various remote locations sharing the files.  I 
want to migrate the data to a new server on a new site, however, i will 
not be able to migrate all the users from the old one to the new one at 
the same time.

So my question is, does anyone know of a tool that can keep the files on 
both locations in sync, even though the same files may be edited 
simultaneously on both ends.  Ideally, i only want the file changes 
replicated (not the whole file each time) and in (near) real time.  
There are lots of tools that can sync two locations, but i don't know 
any that will deal with save conflicts if both files (remote and local) 
was edited, and i don't want to loose either files changes.

This is probably the holy grail of replication, and doesn't yet exist, 
but any tips welcome.  Is rsync capable of this?  I don't mind if it is 
GPL or commercial, Linux or Windows.  Something that has a trail version 
would be useful, as i probably only need it for a couple of weeks while 
we migrate all users. 

Any advice/tips welcome. 
Dj.