Sure, no problem dual booting. How you install Windows 7 will determine where the boot files are for each OS, but just remember the Windows 7 boot files will go on the drive shown as primary in the Bios.
If the Vista drive is primary, then Windows 7 will use the same Boot partition as Vista and you will be ready to go. If you ever decide to remove the Vista drive, it is a simple command to put boot files in another location.
If you make the other drive primary, then Windows 7 will be installed independently and you can use a boot selection to boot to one or the other, or you can use a command to merge the boot files into one.
If you are concerned about causing a problem with Vista, remove that drive until the Windows 7 install is complete.
If you are using an Upgrade version of Windows 7, some of this process will need to be altered. But let us know if you need help, and make very sure you can identify which partition you are looking at.