Oracle VM; whichever version runs on Ubuntu 10.04. I've used free and nonfree versions, and they're essentially the same.

I don't often run it – and it's a very, very stripped down version of XP, with hardly anything on it except for what I absolutely have to use it for. (That said, I find using Guest Additions and shared folders to be absolutely essential… so I can keep it as minimal as possible.)

I've not tried Calligra – hadn't heard of it – but I'm more of a GTK boy. I might try it out later this year; it'll just have to be when I have a chance to deal with a change in workflow.