For Android 4.3 on Virtual Box 4.3.6, System > Acceleration > Uncheck Enable VT-x/AMD-V otherwise you'll get kernel panics.
Easiest process is to install Virtual Box first, start it up, then install GenyMotion on Windows. GenyMotion requires GLIB 2.15 which is not in CentOS6.5 - it is in Fedora20. But GenyMotion did not work inside a Virtual Box instance of Fedora20 because it needed OpenGL 2.0 drivers (or something like that).
Following these instructions works in Windows 7 Professional.
Genymotion on Windows notes:
Use 800x1280 213 dpi resolution settings
FakeGPS Free can set GPS location
Virtual device version doesn't match software version: