I don't know about short-term, but emigration to the US is extremely difficult for UK citizens (But not the Irish for some reason). Essentially it comes down to the catch-22 situation: You can't get a work permit without the offer of a job, but no-one will give you the offer of a job without a work permit.
Unless you have $500,000 to bring in, or a particularly unique skill-set that's in demand, or have immediate family in the US, you're unlikely to get in.
At least that was the situation 10 years ago when I was looking seriously at moving to New Hampshire. It may have changed...