Two X-screens, how to get a window manager on second screen?
I do not think you can run the same window manager at the same time, on the same user, on two X servers. At least you can't do it with most feature-rich wms.
Try running xfwm4 (XFCE window manager) as your secondary wm.
PS: I remember having fun with a compositing enabled Xinerama on a dual card ATI config and xmonad in the past, so I would advice keeping experimenting with that if you are using >=3 monitors.