Get Property Bee for Firefox (web browser) - will show you the price history for that property (or may do if anyone else using Property Bee has ever looked at it).
There is a Which? guide to buying a house - not sure of the exact title - you could get it from Amazon. It may not talk about HIPs if it's not a very very new edition (it does get updated regularly) but still gives you a lot of info. Well worth buying if you're a complete novice to the whole thing.
Work out what 40% off the 2007 price would be, if you can find a 2007 price for a similar house in that road, and offer about there, if you want to be really cheeky - but some are saying that's what the overall price drops could be so it's not totally cheeky. You'd probably end up having to come up from there, but don't start too high as the buyer will probably still expect you to come up in price regardless of where you start.