Friends,You Can Use ROW() function for generating serial numbers,
in A1 cell write
=ROW() and press Enter,that will give 1 as answer.
Now click on A1(i.e. Select it)-> Press Ctrl+Shift+Down(to select the below fields which will get its serial now..) -> After selecting the column Goto--EDIT->FILL->DOWN
This will fill all the cells with the respective ROW number...
U can also use arithmetics with ROW(),if any such requirements are there.
This method is for generating manually.
For automatic ID generation,you can refer to MACROs in excel.
Do put Thanks,if this was helpful because I tried for the whole day to find this....See you..