A few months ago I started a thread asking, if I was applying for a full-time job but actually wanted to work part-time, at what point should I mention hours? There were quite a lot of interesting opinions on this at the time - most people seemed quite negative about it, saying that if they're advertising for full, they want full.
That particular job didn't work out, but I've just been interviewed for, and offered, another one and have successfully negotiated 4 days for what was advertised as a full-time post without any problem at all. I waited until I was offered the post to mention hours at all, and my new employer was very accomodating which was great.
I just wanted to post this, as I'd been feeling quite worried about the prospects of advancing my career whilst still wanting to be part-time (I've recently been made redundant from a fairly high level post in which I'd been working 3 days) but it appears that actually there are possibilities out there, so good luck to anyone else in a similar position, and remember, if you don't ask, you don't get!