What is my tax year for US taxes?

This is confusing me.

I worked in the US from January through March 2005. I then moved to the UK in April, and worked in the UK starting in July 2005.

So to pass the physical presence test, I would say that I was in the UK for the year from April 2005 through April 2006.

However, I am sure that I would have to report my earnings from the US; I can't leave out the money I earned in the US in the first three months of 2005.

So how does this work? Is my tax year January-December? April-April? Or do I have a 16-month-long tax year this year? Which income do I include when I report my earnings? Jan through December or Jan through the following April (16 months)? And what do I do next year? Do I file taxes based on earnings from Jan 2006 through Dec 2006 or from April 2006 through April 2007?

US - Jan - Dec taxyear.  Form 2555 shows Apr-Apr year for the PPT, you will have to wait until April 2006 to file it.  The income will be your UK inc from Apr-Dec.
UK - Apr - Apr taxyear.

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 communication (including any attachments) was 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.

Thanks