Hi,

I was in practical training from January,2008 to September, 2008 with F-1 visa.
But I changed my status to H-1 B on Oct 1st, 2008.
Could you please tell me what tax form to use?
Thank you very much.

Jingle2

When did you enter the U.S. on F1? Are you married? Your citizenship?

On F1/OPT you are exempt from residency for 5-years. You must file non-resident tax return Form 1040NR or 1040NR-EZ and Form 8843. Your income during F1/OPT is not subject to FICA taxes but you must pay federal and state income taxes. On your OPT income you will get deduction based on tax treaty between the U.S. and your country.
Read: Your U.S. Tax Return: U.S. Tax Filing Requirements for Non-Residents