Gaming/Light weight/£600 budget will demand compromise.
I suggest the Acer 6390G range for it's 'smaller screen' (16") and better graphics that normal (9600m GT). You can have that for around £550 online.
I personally compromised and got an Acer 8930G. No regrets with the 18" screen (1920x1200) with 1GB 9600m GT Graphics and plenty of RAM to go around BUT OMG it's huge. No way would I lug it around apart from going between accommodations (uni/home) Incidentally, you can get one of this for £599 (with lower RAM, HDD and CPU) from a well known catalogue store's online sales.