how do we enter values of angles in degrees-minutes-seconds in excel2003 such that we can add two or more cells and perform other functions like multiplication,subtraction etc?

Here's a UDF you can install to give you DMS capability in a simple function:
How to convert degrees/minutes/seconds angles to or from decimal angles in Excel 2000

Or, if you don't mind a geeky looking formula:
Decimal Degrees to Degrees Minutes and Seconds - MrExcel Message Board