Function for validating the Alphabets using javascript

Function for validating the Alphabets
Description:
                 Using javascript validating form for accepting only alphanumarics its a function in script tag .call that function name in textbox  onkeypress="return  Alphabets(event);"



 function Alphabets(nkey)
        {
                var keyval
                if(navigator.appName == "Microsoft Internet Explorer")
                {
                keyval = window.event.keyCode;
                }
                else if (navigator.appName == 'Netscape')
                {
                  nkeycode = nkey.which;
                        keyval = nkeycode;
                }
                //For A-Z
                if(keyval >= 65 && keyval<=90)
                {
                        return true;
                }
                //For a-z
                else  if(keyval >= 97 && keyval<=122)
                {
                        return true;
                }
                //For Backspace
                else if(keyval==8)
                {
                        return true;
                }
                //For General
                else if(keyval==0)
                {
                        return true;
                }
                //For Space
                else if(keyval==32)
                {
                        return true;
                }
                else
                {
                        return false;
                }
        }// End of the function