Many thanks for your comments and contributions. To some extent
dual-boot would seem the way to go. I read elsewhere that
virtualisation slows a machine down by something like 25% which isn't
surprising when one considers that windows and an app are running. A
lot of people use virtualisation for testing systems and driving
hardware from it isn't likely to work. A newish machine is required
for this - mine is a 2.6 Ghz 700 ish mb (about 4 years old), although
i also use ubuntu running on a compaq P3 512mb and that runs fine.

A spare hard drive is also tempting use! I like to keep all working
files on a remote hard drive and have a system hard drive... had a bad
experience with windows years ago before i backed up critical files
with a CDwriter! This also allows one to just plug a remote drive into
any PC.

So i'm going to put two spare older hard drives in the PC robbing its
large one for remote use. But now i'm unsure of how the dual-boot
works. You're supposed to install windows first... but i can't see how
you ensure ubuntu installs to the other drive or partition.