I've been giving it thought for a while. This computer has two HDs fitted inside, but both jumpered 'Master' because one of them has a virus I can't remove, so it has the power plug pulled.
My ultimate plan is to fit the power connection with a double-pole, double-throw switch, to give me Linux on one HD, and XP on the other.
There are two positives going into HDs, one of them carrying considerable amperage.
If I have to power down to change distros, one WILL be powered down.

I'd like to solicit comment on the switch idea.

The magazine APC (Australian PC) usually has at least one, sometimes two, varieties of Linux on every coverdisk.