Making Windows files inaccessible from Ubuntu

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http://askubuntu.com – I've installed Ubuntu on a PC with Windows 7. Now since I want to make that PC a VPN server under Ubuntu I've made the login require no password (Windows still has a password). This makes it easy for anyone to see my Windows files. Can I make them inaccessible (and not visible) from Ubuntu. Sort of like making Ubuntu and Windows two separate systems with their own files on the same hard drive. Thank you! :) (HowTos)