Ski or snowboard? Which is easiest / best for an absolute beginner?(think bambi on ice impressions ...)
Either really. My personal experience was that boarding was quicker, if a bit more painful, to learn. YMMV
When to go? Christmas is appealling, as it would be a fun way to spend the festive period, but would January be better (quieter / cheaper / more likely to have snow)?
Mid January is often very good because it's still low-season, it should have snowed a bit by then, nice and cold (which is good for keeping the snow nice), not busy and cheaper. Christmas can be a bit more risky for decent snow, but you can get lucky - I've experienced great conditions Mid December, for example.
Where to go? Good for beginners? Early snow if I go at christmas? Not really after the biggest party town as I'd rather focus on the skiing, but a nice bar or two would be good. Is Austria / Italy cheaper than France?
France is the most expensive in general. Le me point you to a detailed factual survey carried out by the acknowledged industry experts (no arguments please TJ): WTSS RPI
As a learner, the key thing you DON'T need is a big linked ski resort. This opens up many options that the majority of intermediate and advanced riders overlook. And smaller resorts a significantly cheaper for everything, esp. lift passes. What you are looking for is a place with a decent school, plus lots of blue graded trails to develop on, accessed by chairs/bubbles. It's worth also considering a decent village/town for days when you want a rest! This may help: The bit at the bottom left. They have a resort short-list chooser widget coming soon. When it appears, I try to remember to link on this thread. In the mean time, you could buy the book - it's very good.
What companies do 'learn to ski / beginner' weeks for solo guests? (Would be nice to share the holiday with a group of people who are also learning at the same time)
You could try getting into a catered chalet or chalet hotel. Groups often fail to fill-up large chalets and chalet hotels and the extra rooms can get sold at a cheaper price closer to the holiday date - teletext often carries this kind. Travelling solo, groups can take you under their wing! When you take lessons, you will be put in a class with other newbies. When I've done lessons back in the day, a few were usually happy to have apres drinks and socialise a bit
Is it worth practicing the basics on a ski slope here (the one near me has a 'perma snow' slope and offers classes for beginners)? I know is apparently not the same as snow, but might it teach me the 'how to put you skis on / basic moves etc?
If you have time and money, why not!? Personally, I don't get on with synthetic, but that's just me.