I graduated in December of 2008, and now I am working and doing my OPT. One attorney told me that I don't have to pay taxes (medicare, ss, federal and state), and nether my company.
I would like to know if this is true?

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 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