This is where you should go: http://sourceforge.net/projects/backuppc/files/cygwin-rsyncd/
Packaged rsyncd for Windows and instructions included!
Have fun!
Minimal setup: (backuppc server side config):
$Conf{XferMethod} = "rsyncd";
$Conf{RsyncdUserName} = "userfromotherside";
$Conf{RsyncdPasswd} = 'betterpasswordthanthisone';
$Conf{RsyncShareName} = "cDrive";
Other side (Cygwin setup):
in c:\rsyncd\rsyncd.secrets
userfromotherside:betterpasswordthanthisone
in c:\rsyncd\rsyncd.conf
check and set:
(match bits from above - rsyncd.conf has most of this already...)
This assumes you wan't to back up the full c drive from the cygwin mount point.
[cDrive]
path = /cygdrive/c/
comment = Entire C Drive
strict modes = false
{RsyncdUserName}
auth users = userfromotherside
secrents file = c:/rsyncd/rsyncd.secrets
hosts allow = ip list comma sep of Backuppc server(s)
read only = false
list = false
Now, finish with some tweaks to the Windows firewall:
File and Printer Sharing (Echo Request - ICMPv4-In) And pick the rsyncd program as well.
Finally, reload the config in Backuppc (Admin Options -> Reload)