Even ignoring your criminal record, UK citizens generally have little or no chance of moving to the USA.
UK passport holders are not eligible for the 'green card lottery'; so you can only move to the USA if you've got close family members there, or you've got exceptional talents that can't be matched by a US citizen (e.g. if you're David Beckham), or you've got specialist professional qualifications at advanced degree level, or you've got a minimum of 1 million dollars to invest in setting up a new business which will create jobs:
http://www.usembassy.org.uk/cons_new/visa/iv/i ndex.html
Marrying a US citizen might help but there have been recent posts, here on AB, from someone who has done so but has been waiting for over 2 years to find out if they'll be granted an immigration visa. (As far as I know, that person hasn't even got the complicating factor of a criminal record).
The US immigration system has a rather strange attitude to criminal offences, as it seems to value property above people. The emphasis is upon crimes of 'moral turpitude', which normally bar anyone from entering the USA (even as a tourist). 'Moral turpitude' includes all crimes of dishonesty (such as nicking a Mars bar) but excludes some violent offences (such as punching someone):
http://en.wikipedia.org/wiki/Moral_turpitude
If you've ever been convicted of a crime of moral turpitude (unless it was very many years ago), you're chances of obtaining an immigration visa are extremely low.
Chris