it's pretty hard to do...i'm looking into it too at the moment. Been emailing companies (with no replies as yet). To get a job you need to get a company to sponsor you for a work visa. but they can only employ a foreign 'alien' (as we're called!! nice!) if there are no suitable US applicants. Also, i heard it's illegal to go out there and look for a job, so you'd need to set one up before you go out there. Also, our normal visas only cover us for 90 days (3 months) so you can't just go out there for 6 months as far as i know.
Saying all that, it's not impossible to find a job, a friend of mine managed it a few years ago by going out there for a hol and applying for a job, got an interview and they decided to sponsor her. so maybe it's not illegal to look for work, just what i heard from someone...worth checking out.
Best to look on us embassy website for london office which has lots of info on visas and steps to take.
Good luck, and let me know how u get on!!!