I've personally had bad experiences with Dabs, so would recommend Scan - but that's just me.
Anyway, looks like a few I3 or I5s in your budget range:
http://www.scan.co.uk/Shop/Computer-...lus-Display-i5
Asus K72F-TY201V 17.3 i3-330 4GB 320GB Windows 7HP DVD Super Multi - this is sub £500
There are a couple of others just over £500, but don't include Windows (so add another £60 or so for Win 7)