On the contrary, Vista is probably o.k., but the Debian install over-wrote the MBR of the original disk.
1) Is there any way to get grub to boot windows with only the original hard drive and windows partition ?
1) Is there a rescue mode command I could type, I can inspect the grub config files on the 2nd disk ?
1) Not worth the effort - you would have to find a partition for grub, or use something like grub4dos.
2) Boot Debian and use the applicable grub recovery commands to install to the second disks MBR. Might be grub-install and update-grub - check the Debian doco.
Then pull the second disk out, boot the Vista install/recovery CD and get into recovery centre, and recover the MBR .
Then the box should boot as normal without the second disk, and the second disk should boot if installed and selected as the boot disk from the BIOS.