If you have Windows 7 beta in a dual boot system along with Windows Vista then probably you might want to update or upgrade it to Windows 7 RC. There are two options to upgrade to Windows 7 RC. The quick way is to fool the installer by changing the MinClient build number to 7000 as explained in Engineering Windows 7 by MSDN.
But the best way and suggested way is to do a clean install of Windows 7 RC. Or you might want to upgrade Vista and just remove the Windows 7 beta. In any case here is tutorial on how to safely remove or uninstall Windows 7 beta from Dual boot system.
Note: Before removing the Windows 7 from the partition, you may want to save the Windows 7 settings, files and users to transfer to the new Windows 7.
The quick way to remove the OS from a partition is by going to System Configuration.
Go to Start –> type msconfig –> Click Ok, if UAC prompts.
Go to Boot tab and click on Windows 7 and click Delete.
To be on the safe side, I recommend using the freeware to manage the Vista Bootloader. I personally use EasyBCD, if I want to install other OS including Ubuntu or Fedora or other linux OS. This gives a better control of the boot loader.
Under view settings, you can view the OS currently in the MBR (Master Boot Record)
Go to Add/Remove Entries and choose Windows 7 and click Delete.
Go to Manage Bootloader and choose Reinstall the Vista Bootloader and click Write MBR. This will overwrite the MBR so that you dont have any issue with removing an OS from the boot loader.
Now that the Windows 7 has been removed, you can format that partition.
Its similar to post where we saw how to partition in Windows Vista. Go to Start –> Type Computer Management –> Go to Disk Management. Right click the drive where Windows 7 was installed and click Format.
Now you can either use that partition to clean install another OS or Windows 7 or you can delete that partition and extend it with another partition.