Dual monitor (HDMI and DVI, two LG22W) on Acer X1700 seems to be a problem with the open source drivers.

To get them working (extended desktop, not mirror) just follow the guide:

1. Run the following commands:
   Code:

   wget --no-check-certificate https://www2.ati.com/drivers/linux/ati-driver-installer-9-5-x86.x86_64.run
   chmod 755 ati-driver-installer-9-5-x86.x86_64.run
   sudo ./ati-driver-installer-9-5-x86.x86_64.run --buildandinstallpkg Ubuntu/9.04
   sudo aticonfig --initial -f

2. Reboot the system
3. Use System > Preferences > Display to detach the monitors from each other, and set the proper resolution
4. Log out, and back into the system

Source