DropDownlist event is not firing

Question

Hi, I am relatively new to .NET framework but I've overall 3 years of web development experience using Java and php technology. I am right now using VS.NET 2002 with .NET version 1.0 to develop my application. I've a dropdown list server control which gets automatically populater from the database. I want to do so addition , subtraction and lil bit manipulations on the page itself when somebody selects an item from the drop down list. I tried to use selectedindexchanged event handler and by keeping autopostback=true but it doesn't seem to work. Even i kept a break point but the event doesn't get fire at all. Even i tried to use onselectedindexchange method but it also doesn't work. So Please help me out guys. I read almost everything related to dropdownlist alreayd but nothing seems to help me. Thanks in advance,