Dual boot Xp/Vista on 2 hdds. If one HDD fails, can I still boot?

I am getting ready to build a dual boot system (2 hard drives) with XP on one and Vista on the other. If one HDD fails, (or removed)how would I boot to the other?

Thanks!!

I prefer to install each OS separately (only one connected HD drive at a time) and use the BIOS boot menu. The drawback is that I can not see which OS is installed on which drive (no big deal). But on the plus side, I can add or remove the drives as I see fit.

that's right. On my MoBo, I use the "F11" key to call up a boot menu showing all available boot devices, yours might use a different key, or may not have the feature at all. Find out if it has it, because if it doesn't you'll have to enter the BIOS everytime you want to boot the second OS (and that would get old quickly). If that's the case, you'll be better off installing the OS with both drives connected, XP first and Vista second.