Re: Have 2 HDs. Want Vista on one and Ubuntu on the other.
Strongly support the approach that darkod recommends -- in disconnecting the other drive while installing Ubuntu. That will prevent any "accidental" overwriting of anything on your Vista drive.
When you install Ubuntu to its own drive, it will install GRUB there as well. But when you reconnect the Windows drive, you will have to use the BIOS to select which OS, because GRUB will not have an entry for Windows.
Have you considered that you can configure GRUB as follows:
1) Have the default selection being Windows
2) NOT show a menu when booting.
That accomplishes what you want (Windows by default) but still leaves you the option of holding down the SHIFT key when you boot and selecting Ubuntu when the GRUB menu displays.
Ubuntu 15.04 Mate, Mint 17.1; MS Win 8.1, Win10 TP.
Will not respond to PM requests for support -- use the forums.