Serial Number Generation Avoiding Duplicates

Question

hi i have a datagrid, and i have binded it to a dataset, i have a column called srno and its autogenerated, it works fine,

the problem is when i enter the data for the first time in a row the srno is 1, after entering the data i navigate to the second row,  at that time srno is 2, before entering the data in the 2nd row  do some alterations in the first row, after finishing alterations in the 1st row i return back to the 2nd row, and suprisingly the srno is now 3,

im using windows application 2003
need help???

thanks

Prasenna