Hi all,
First, I just want to say thank you. I've read quite a lot on this forum and have learnt so much before I even own the car - you truly are a friendly and knowledgeable bunch!
Secondly, the comments from Jonathan and Legend-ary about the rust on the sunroof have given me pause - I don't want water leaking through the roof! I've seen three Jazz's now (2002 50k, 2003 80k and 2005 90k) all for around £1,500. They've all driven fine with no odd noises, looked in good mechanical condition and had working AC. The 2002's mileage was attractive (and it already had an aux cable!), but was in poor cosmetic condition inside and out. The 2003 one was the one with the broken radio and rusty sunroof, but otherwise in good condition. The 2005 one was a bit so-so, with odd things broken and scuffed and I didn't like the colour. So given what you've said I've decided to hold fire as I can wait another couple of weeks until I really need one. There's another 2002 model with 70k just come available in the same price range which looks in good condition, so I'll go take a look at that.
Third, thanks very much to TG and Legand-ary for the comments about the radio. TG, depending on what I eventually go with, I might be in the market for an inline bluetooth aux adaptor! Sitefive, the website I linked to in the first post does give a fix for the radio, which involves soldering on the circuit board and maybe a couple of new (cheap) components, but without having a Jazz to poke around in I can't be any more specific about what needs doing.
All the best.