A PC with Windows Vista can be used for installing Windows 7 with Dual boot option. In order to have dual boot the pre-installed windows vista PC must have a separate partition for installing Windows 7 Release Candidate (RC). If a new partition does not exists then you can use refer page for creating a new partition in Windows Vista.
After creating a new partition, register with Windows Live Id and download the setup. Now create a new DVD using the downloaded Windows 7 Release Candidate ISO image. Insert the DVD in to your DVD-ROM Drive and restart your PC. Windows 7 files will be copied to your system and when the installation requests for the partition, make sure to the select the newly created partition. After setup is complete your PC should be have the following bootable options
- Windows 7
- Windows Vista