function displayTemp(form) {
     var tempVal, finalC, finalF, finalTemp;

     if (form.TC[0].checked) {
          tempVal = form.yourInput.value;
          finalC = (tempVal - 32) * (5 / 9);
          finalTemp = Math.round(finalC) + " degrees Celsius";
     }
     else {
          tempVal = form.yourInput.value;
          finalF = (tempVal * (9 / 5)) + 32;
          finalTemp = Math.round(finalF) + " degrees Fahrenheit";
     }

</SCRIPT>

<FORM>
     <INPUT TYPE="text" NAME="yourInput" onChange="displayTemp(this.form);">
     <INPUT TYPE="radio" NAME="TC" onClick="displayTemp(this.form);" CHECKED> Fahrenheit
     <INPUT TYPE="radio" NAME="TC" onClick="displayTemp(this.form);"> Celsius
     Is equal to:
    <INPUT TYPE="text" NAME="result">
</FORM>