Route NAS traffic through a VPN

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http://serverfault.com – I have a motorola NVG510 router which connects directly to the internet via AT&T. I recently purchased Zyxel NSA325 NAS. I connected the network attached storage directly to the router. I was wondering if there is a way to route all incoming traffic to the NAS over a vpn like air vpn. The purpose is to encrypt all traffic to the NAS. Can I do this with my existing hardware or do I have to get another router to set up a vpn? (HowTos)