Backup offsite on a win machine... how to access?

[Outsider]

I'm planning on setting up an offisite storage location at my parents house. Their computers are running 24/7 already, so this would give me good availability.
I am planning on doing a full backup of my data on a HD, and attaching that drive to one of their machines.

My question is about how to access the machine with the HD to do automated nightly incremental backups.
I am running linux on my home machines, and if they were also running linux, I could just run a rsync over ssh, and all would be dandy, but I don't know what I can do to connect to a win machine.

Any ideas?

[Justin C]

PPTP VPN to connect and then use RoboCopy to sync?