Thanks your help. But I am still confused by my status for 2005 tax return.

I came in USA on July 9th, 2001 from South Korea. I stayed all year 2002, 2003, and 2004 in USA.
I am on H1b from November 1, 2005. I was on F1 until September 31, 2005 on OPT. I got this job on April 25, 2005.

According to the Substantial Presence Test, I believe I am a resident alien at the end of 2005 tax year. So, I am a Dual -Status alien for 2005. Am I right?

In this case of a Dual Status alien, which forms, 1040NR or 1040, are more benefits for my tax return?

If filing 1040, am I eligible to get SS and Medicare Tax because my employer has deducted my SST and Medicare Tax since I worked on April 2005 on OPT (F1)?
I plan to claim Form 843 to get these tax refund soon.

Also I am confused with “First Year Choice.” Does “First Year Choice” affect my tax return? If so, what should I do?

Thanks in advance.

You are dual status.

A dual-status return requires you file both Form 1040 and 1040NR.

The First Year Choice is an alternative to filing a dual-status return. It allows you to file just a Form 1040 after you meet the Substantial Presence Test, which, for you, would be after 20 June 2006.