does ubuntu allow extended desktop

I currently have windows 7 starter which does not allow for extended desktop, meaning I cannot run dual screens. Does ubuntu support this?

Yes, Ubuntu does support a desktop extended across multiple monitors by default. Just today I brought in my Thinkpad with Ubuntu 13.04 (Unity) to work to try out with 2 external monitors and both were properly detected immediately. In the "Displays" settings you can configure them to your liking, as shown here:

You can get to Displays by simply searching for it in the dash, or by going to System Settings > Displays. Your mileage may vary based on your graphics chipset. For example, an Nvidia chipset may have its settings in a utility provided by Nvidia instead of being fully configurable from this interface. In my example, the chipset is an Intel HD4000. Also be aware of how the performance capabilities of your graphics card will affect overall graphical performance across an increasing number of monitors with high resolutions.

Yes Ubuntu does have multi-monitor (extended desktop) support out of the box. Although this will depend on your hardware and if it can run it comfortably.

Multi-monitor support is a feature that Microsoft left out of Windows 7 Starter.

You can see the limitations of Windows 7 Starter here.

Windows 7 Starter does not include:

• Aero Glass, meaning you can only use the Windows Basic or other opaque themes. It also means you do not get Taskbar Previews or Aero Peek.
• Personalization features for changing desktop backgrounds, window colors, or sound schemes.
• The ability to switch between users without having to log off.
• 64 bit version
• Multi-monitor support.
• DVD playback.
• Windows Media Center for watching recorded TV or other media.
• Remote Media Streaming for streaming your music, videos, and recorded TV from your home computer.
• Domain support for business customers.
• XP Mode for those that want the ability to run older Windows XP programs on Windows 7.