The good news is that you are asking your questions before you move. This gives you time to plan your course of action.
Tips for going-to-move:
1) The year you move, you file a Form 1040 with a Form 2555 Foreign Earned Income Exclusion. Form 2555 may require that you file in May of 2007 (a year after you move) or even as late as January of 2008 (a full calendar year after you move).
2) If you work for a UK employer, they will withhold UK National Insurance (NI). Our US/UK Totalization Agreement means that you won't owe any US SS on top of the UK NI.
3) If your UK income is in excess of $80,000 annually, you can also file Form 1116 Foreign Tax Credit in the US, which in most cases will reduce any remaining US tax down to zero.
4) If you move permanently, you usually will no longer be subject to state tax. There are many exceptions, however, so take the precautions necessary to sever ties with Illinois.
5) The UK tax can be reduced if you are NonDomiciled. You may wish to read up on the definitions of Resident and Domicile at
http://www.hmrc.gov.uk/pdfs/ir20.htmGood luck!
IRS Circular 230 Disclosure: To ensure compliance with requirements imposed by the U.S. Internal Revenue Service, we inform you that any tax advice contained in this posting (including any attachments) is not intended or written to be used, and cannot be used, by any taxpayer for the purpose of (1) avoiding tax-related penalties under the U.S. Internal Revenue Code or (2) promoting, marketing or recommending to another party any tax-related matters addressed herein.