Hello,
I'm a Russian citizen. I've been in the US for almost 8 years. I've got a F1 status from 11.19.2003 till now. At this year, May 2008, I graduated from the University and got my OPT from June 1, 2008 for one year. At the same time, I've been approved for the H1B visa from October 1, 2008. I am about to start work for the NYC company at August 12, 2008. So with all this information could you please tell me that in case of tax treaty can I apply for any and how? Am I eligible for them at all in situation that I’m going to hold OPT for 1.5 month and working visa for 3 month during the year? The info at the IRS web site is too broad; I just want to have someone who could answer me in person, please. Thank you for your help!

Every one F1 or OPT is exempt from residency for 5-years. You have already completed 5-years so during 2008, your days in the U.S. will be counted towards residency.
For 2008, you will file resident tax return. Even your OPT income (and also H1-B income) is subject to Social security and Medicare taxes.