I believe I fall under the resident alien category (as per substantial presence test). I recently got my H1B approved. I was under F1-OPT-F1 visa till now. I 'm just wondering what taxes am I exempt from? Also, what forms beside w-4 do I need for tax purpose? Any advice would be greatly appreciated.

On F-1/OPT you are exempt for 5-years. Only your days on H1-B count toward SPT. So if you are not married, you will file nonresident tax return for 2009.