I was talking about unison a few posts ago (and a long time ago).
I finally got round to trying it under windows. I was a little hesitant at first, as it required installing a windows port of the linux OpenSSH program, which has to be run under Cygwin (which allows specially compiled linux programs to run under linux).
In the end, installing Cygwin was dead simple. And to get Unison to work, all i needed to do was edit the windows path (right click My Compter -> properties -> Advanced tab -> Environment variables -> PATH) and add the directory for Cygwin in it…
The unison help manual on their website gave clear instructions.
If anyone else has a linux box they can ssh into and wants to use it to synchronise files, it is dead simple!
If you have a windows box and want it to work across the internet, I am sure Cygwin has a windows port of an ssh server… so you could try that, though it could get complicated with file conversions (but it is probably worth a try).