How to backup NAS using Time Machine I just purchased a new Iomega NAS IX2-200 4TB. I need to regularly backup this NAS. Time Machine would be the best option. How do I setup so the Time Machine will backup this NAS to my external Hard Drive? 

I don't want to backup my Mac, that's already been done on the Time Capsule. Instead I just want to backup my NAS drive. But I'm not sure how to go about this, as the NAS is a network drive.
I wouldn't use Time Machine for this, it is best at backing up your local Mac. The NAS you have has a built in backup function that can use a local USB drive or a network share (as well as other options). So if you want to backup the NAS to a drive mounted on your Mac just set the share up on the Mac then configure the NAS to backup to that share on a schedule. If you really want to use Time Machine you would have to mount the NAS or more likely specific directories on the NAS then include those in Time Machine on the Mac, This article gives good info on backing up several types of network shares to your Mac thru time machine: http://lifehacker.com/5685547/how-to-set-up-time-machine-to-back-up-to-a-networked-windows-or-linux-machine