Ubuntu :: Dual Booting From EHD - Fallback If Drive Not Found?

I have managed to get a system going where I have kubuntu installed on a partition of my external hard drive. When the ehd is plugged in, everything works well. I have the option to boot into vista (my main os) or kubuntu. However, I see no reason why it won't let me have some kind of fallback mechanism that would let me boot into vista if the ehd is not found, instead I end up with the grub rescue prompt.

If not then I'm going to have to look at other options, perhaps booting into vista by default unless I hold down escape or whatever other key my bios expects to override, because there will be times that my ehd won't be plugged in. This is the only little niggle, as apart from that everything is working great.