I have an ASUS RT N16 router and 3 computers on my home network, two of which are wireless. I want to backup and share files on an external hard drive do I need a specific type of hard drive and special software?
No. You can set up an internal or external drive on any computer and set the permissions on it so that it is shared then any computer on the network can read/write to it. If you are not familiar with simple networking, a turn-key NAS (network attached storage) may be better for you.