How to backup Mac and Windows computers to shared network drive?

I am considering getting an external hard drive like this one, which you can plug into your wireless router and then computers on your network can back up to it. It says it supports both Mac and Windows, but I assume it comes formatted as NTFS. Would I need to re-partition the drive and create 2 partitions - one NTFS partition for my Windows computers, and one HFS+ partition for my Mac? Or does it somehow support both Mac and Windows computers out of the box?

Networked drives are a little different that drives that are directly connected to the Mac itself. Networked connected drives do all the work so OS X doesn't need to know or interact with the filesystem. In other words, the filesystem of the networked drive is irrelevant since all the filesystem related work gets done by the drive itself. Most network connected drives have server software installed that manage the shares, software which will setup the required layers that effectively make the underlying filesystem irrelevant to you and your Mac.

Thus, the drive could be formatted as an NTFS, FAT32, ext4, etc. drive - all of that is irrelevant to OS X if the drive is a network one.