What amount will be taxable?

Dear all,

I want to know from when I will require to pay the service tax 

The question is like this. 

I own teaching institute and have recevied contractual work of 17 lakh.

I will be required to issue three bills to receive this amount.

The amount of one bill will be 566666.66(five lakh sixty six thousand six hundread sixty six rs.) 

I will get amount of two bills within 31st march 2013, and third bill will be cleared after 1st april 2013

that means for this financial year the amount of two bills will be 1133332.00(above eleven lakh)

I have already registered my firm for the service tax and this is the first time the annual turn over will cross above 10 lakhs.

now my question is on what amount I will require to pay service tax?

and is service tax excemption limit is given for every year ? or after crossing 10 lakh , on every bill amount I will require to pay service tax.