can you be slighly more specific than 1.4 GHz processor?
A 1.4 centrino is about the same as a 2.2 p4 and athlon state their processor speeds relative to the p4.
The centrino has the longest battery life and they can keep these laptops the lightest, the Athlon mobiles have a slightly shorter battery life but are more or less comparable in weight. However the athlons are a lot cheaper. (however they don't always have wifi capabilities, but that can be added later)
Do you want to play games or are you interrested in a good graphics card? If not it generally expands the amout of available laptops. You could for example check ASUS.
It's important to look at the speed of the HDD I would go for at least 5400, otherwise it will lagg your system.
They're quite cheap and have a decent offer of laptops, be sure to check the jewel systems, you can configure these and their quite light. On the other hand I think their design could be better. (I don't like the grey/silver lid holding the screen)
I won't go into specific makes or models simply because some people on this forum are dell fanboy (for example) and some seem to hold a grudge against acers.
I have no experience with these makes but I have noticed that dell, hp/compaq and some other major companies are doing some major overcharging in europe. They seem to be doing this less in the US. (I checked this by comparing prices to those in europe and checking the prices relative to other companies: ACER vs DELL) If I lived there then I might recomend them. However as I (and I presume you too) am on some sort of a budget adn don't live in the US I'd stay away from them.
I don't think you'll be able to get a dvd-rw in a system that costs <1000 pounds. Most centrino based notebooks should be light enough to carry around easily but unfortunately they're quite costly too. Toxicogen is right. I've noticed that Dell tends to overcharge in the UK. I checked and compared the prices since I'll be heading there late next year.