you dont get the taxes back.
The OPT is just a privilege for international students to work after they graduate and get some hands on experience. it has no any whatsoever tax advantages.
Just pay the taxes. i am sure down the road u will look for H1 and eventually stay here, so its wise to pay taxes from now. Depending on how much you make, and how many dependents you show in your W2, in April 07 when you file taxes you might get some money back. but please remember that money is not just the excess money that you had paid in taxes.
let me ask you a question....if you're working hard..and you come home one day..and you get really sick..and you call 911...do you want the damn ambulance to come over at your place and take you to the hospital..........well if you do...then pay the taxes.