I'm looking to spend around 400 pounds (750-800$) on a laptop.

I'm not worried too much about 3d performance, fast cpu's, or screen size, but i wouldl like it to...

Have a huge battery life
Good wireless capabilities

I'm prepared to order bits individually and even go as far as using Flash memory in order to boot the thing up, so long as I have 16 gig of space.

Aside from buying more batteries and not running demanding applications, anyone have any good advice on what factors can I address to give me a long battery life?

I'm hoping for 5 + hours of constant use, surfing net, using MS office, a few downloads in the background etc?