A bit of a sideways step.

When I had a motherboard which would support two HDs, I WAS going to have two, but separated by a double-on switch in the front of the case.

The idea was, XP on one HD, Linux on the other, one for work, one for fun and the web.

It would take some soldering to the power connection, and on course, a shutdown to change, but no-one told me it was unfeasible.
The switch is a three-circuit double-on, and was available readily at a local electronics house.
My motherboard died before I got around to trying it, and the new one won't support two HDs.