if you are running osx or linux, you have to buy an older model of the xbox 360 kinect. The newer models and kinect for windows has firmware updates that prevents communications from being opened between the kinect and the computer. If you are using a PC any kinect is fair game.
As for system requirements here is the specs straight from microsoft -https://msdn.microsoft.com/en-us/library/hh855359.aspx
Hardware Requirements
Your computer must have the following minimum capabilities.
32-bit (x86) or 64-bit (x64) processors
Dual-core, 2.66-GHz or faster processor
USB 2.0 bus dedicated to the Kinect
2 GB of RAM
Graphics card that supports DirectX 9.0c
A Microsoft Kinect for Windows Sensor
The graphics card and sensor you can ignore but I can tell you that slower cpus struggle to maintain proper framerates from my past experience. The requirements for a kinect 2.0 are slightly different. If you can I would highly suggest using a PC for kinect since the drivers are native and the install and api is super easy to use. ofxOpenNI and ofxKinect are ok but can be a serious pain in the ass to get setup a la - http://forum.openframeworks.cc/t/skeleton-tracking-without-calibration-psi-pose/20488
There has been a lot of work on opening up the kinect to other systems but if you are going to invest time and money in it a PC will make your life way way easier. Openframeworks is essentially the same between OS's anyways so there is no particular reason that you should use osx or linux for kinect development unless that is the system you are already working with and dont want to get new hardware. Plus kinect 2.0 support so that your not stuck with only using old sensors.