Better to go through the provisions form the act or any other material, it is very difficult to explain it here. However, the following example may help u i guess:
Suppose, my Total Income is Rs 3,25,000/- pa and i file return today i.e on 26-08-2008
Tax + Cess thereon will be Rs 47,895/-
Int u/s 234A: 1% pm or part thereof from the due date to the date of filing retun i.e. 1%*47800*1month = 478
Int u/s 234B: 1% pm or part thereof from the first date of financial year end (1-4-8) to the date of payment of tax(26-8-8) 1%*47800*5 months = 2390
Int u/s 234B: For deferrment of advance tax 47800*30%*1%*3+47800*60%*1%*3+47800*100%*1%*1 = 1769