[xmonad] Screen workspaces not working on new Ubuntu 8.04 amd64 install

I was using Xmonad quite successfully on Slackware 12 and 12.1. However, we were recently forced to switch to 64-bit Ubuntu 8.04 at work. Under Slackware I was able to have a separate workspace on my left and right monitors. With Hardy I have a single workspace that spans both monitors. I've even gone so far as using the same xorg.conf on both and the hand-built Xmonad I was using under Slackware, yet the behavior persists. Comparing the xdpyinfo output and the xorg.0.logs the only major difference that I see is Hardy has DRI working and a few newer versions of some X modules. I am at a loss as to what could cause this. But it makes Xmonad useless to me and I'm dying in Gnome. Please help.