I'm dual booting Windows 7 Ultimate x64 and Ubuntu 9.10 (Karmic Koala) x64 on a Lenovo Thinkpad T61p laptop.  I installed Windows first, then Ubuntu, and then updated the boot loader to default back to Windows.  The following list describes getting Ubuntu up and running, which was surprisingly easy.

1. Get the latest updates.  System -> Administration -> Update Manager.
    
2. After reboot it was obvious there were problems with the display driver.  The screen was choppy and flickered but luckily it was usable.  I browsed to System -> Administration -> Hardware Drivers and was pleased to see a few Nvidia graphics drivers waiting to be installed.  After installation and a reboot, video playback has been crystal clear.
    
   
    
3. Verify software sources are correct.  The top 4 sources should be checked.  System -> Administration -> Software Sources.
    
   
    
4. Reload the Synaptic Package Manager.  If you don't do this, you may encounter problems when trying to locate and download packages through the package manager or the Ubuntu Software Center.  System -> Administration -> Synaptic Package Manager.
    
   
    
5. Install the Ubuntu Restricted Extras package.  Applications -> Ubuntu Software Center and search for restricted.