[xmonad] Dual-Monitor setup with GNOME (Help!)

Hi all, I scored an extra monitor at uni but am having trouble setting it up with xmonad. Normally I use xmonad with gnome. When I connected the second monitor and configured xorg.conf with Xinerama, the second monitor just shows the background and I can't move any windows into it. I can move my mouse into it and select things from menus in the gnome bar, but the windows always appear on the primary monitor. (Also, the second monitor appears to have a second mouse, with a cursor that looks like an X, not the gnome cursor.) I'm on Ubuntu 9.04 with xmonad 0.8. The video card is ATI Radeon HD 3450 (using fglrx). Please help. I don't want to give up xmonad just to use the second screen. Alex