OK, after a bit (READ: waaay too long reading and googling...) of
investigation, I've found a solution which works for me.

Basically I tried everything I could think of to get the SSH2 client
from SSH.com working with the rsync app, and nothing would work. So, I
switched to using OpenSSH, and it works perfectly!

I googled for openssh windows binaries (not being the type to buld my
own...), and found version 3.7.1p1 avail
(http://lexa.mckenna.edu/sshwindows/). It took some reading and
messing about to get it to install and run as I wanted it to, but in
the end, all worth it.

I've now got a win client which can rsync using ssh2 to my linux box,
and I am less concerned about MITMs from things like ettercap for now.

Hope this helps,

Adrian