You can purchase a Windows 7 Upgrade DVD from Dell (Home Premium, Professional, Ultimate) or amazon or any local computer store. The Latitude D Series are Windows Vista compatible and so have Windows Vista Drivers which can be used in conjunction with Windows 7. Before upgrading to Windows 7 you may want to consider a few things: • Memory, upgrade to 4 GB for best performance here (run the crucial scan to see how much you already have). I wouldn't stick Windows 7 on it if you have less than 2 GB, it will still run at 1 GB but not as well. • 64 bit or 32 bit, you will need to run the upgrade advisor to check if the system is 64 bit compatible. For installing Windows 7, I refer you to my wiki A Clean Install of Windows, it will take you through the installation procedure step by step. If you have the bluetooth module, use the Windows 7 Bluetooth Driver R231570 (don't install the Vista driver for Bluetooth).  
Hi, I have a Latitude D531 with Windows XP and was wondering if I can install Windows 7 into it. If so, can I purchase installation DVD from Dell for it?  Thank you
Dell Latitude D531 and Windows 7