Check these guys out..They're new but offer a very decent warranty with a replacement and your money back if it breaks in the first year.
http://www.rizeon.com/notebooks.php
Most are in the £650 bracket and come with semi-decent gfx cards.
I don't know what fps you're likely to get with these cards on oblivion but a 64mb (256 turbocache) Geforce 7400 has given me around 50 -60fps @ 1280 x 1024 on CS:S on reasonably high settings.