I think I am adding more redundant questions but I really can't find a straight answer to this. I know there will be minimum 20000 people like me, I want to see if any one can help. There is conflicting information all over the web and wanted to know from people who did some research.

I came to the US in 2006 on F1 visa. I started working in 2008 feb on my OPT/F1 visa. During this period, I was exempt from medicare and social security taxes. I got through the lottery and from Oct 1st to Dec 31st I am on H1B visa in which I am paying all the taxes.

I am a single without any dependents and never married.

Specific questions I have
1. Should I file under dual status - The sticky note seems to suggest that.
2. Under which staus - resident or non-resident.
3. Will I be able to include tax treaty benefits for the part of income on F1, if yes how shoud I mention this in 1040NR-EZ.

I stayed in the US for 2008- 330 days, 2007-365 days, 2006- 120 days, this is where people are confused. Does the days I am in OPT come under substantial presence test? From the calculators it seems so, but I have contradicting information from this site.. F1, OPT, J1, H1B, H4, L1, TN Visa Taxes, Form 1040NR 1040NR EZ Instructions Software, Form 8843, Form 843, IRS Tax Return Refund , H4 Visa Tax ID Form W-7 ITIN, Non Resident Tax, International Student Taxes, Mailing Address, US Tax Treaty Benefits, O (http://www.visataxes.com)

Last year, one tax consultant did things wrongly(on F1 status) and I have to pay for it now, I don't want to be doing that again.

Any help is appreciated.

You are exempt on F1/OPT, which is up to Oct 2008. On H1-B, you completed about 90 days of residency so you will file nonresident tax return Form 1040NR or 1040NR-EZ with 8843.
If you have income during OPT, you will get treaty deduction.
Read: Your U.S. Tax Return: U.S. Tax Filing Requirements for Non-Residents (http://taxipay.blogspot.com/2008/03/us-tax-filing-requirements-for-non.html)

Thanks for the quick reply :)

Can I also claim the exemtion deduction line 13 for a single? (which I think is 3500)

Yes, you get to claim the $3,500 personal exemption.