It's just an HTML file with some JavaScript. Just copy the text in the Quote and save it as a .htm or .html file on your PC in the location of your choice and open it with your browser (which should be the default behavior anyway).

QUOTE
<HTML>
<HEAD>
<SCRIPT LANGUAGE = "JAVASCRIPT">
function Calculate(what){
 if(document.CALC.touchedlast.value==""){
  err("wrong")
  return
 }
 if(what=="temp"){
  if(document.CALC.touchedlast.value=="celsius"){
   if(isNaN(document.CALC.celsius.value)){
    err("temp");
   }else{
    CtoF(document.CALC.celsius.value);
   }
  }else if(document.CALC.touchedlast.value=="fahrenheit"){
   if(isNaN(document.CALC.fahrenheit.value)){
    err("temp");
   }else{
    FtoC(document.CALC.fahrenheit.value);
   }
  }else{
   err("wrong");
   return
  }
 }else{
  if(document.CALC.touchedlast.value=="mm"){
   if(isNaN(document.CALC.mm.value)){
    err("length");
   }else{
    MtoI(document.CALC.mm.value);
   }
  }else if(document.CALC.touchedlast.value=="inches"){
   if(isNaN(document.CALC.inches.value)){
    err("length");
   }else{    
    ItoM(document.CALC.inches.value);
   }
  }else{
   err("wrong");
   return
  }
 }
}
 
function err(type){
 if(type=="temp"){
  alert("The value you are trying to calculate is not a number.  nPlease try again.");
  document.CALC.celsius.value="";
  document.CALC.fahrenheit.value="";
  document.CALC.touchedlast.value="";
  return
 }else if(type=="length"){
  alert("The value you are trying to calculate is not a number.  nPlease try again.");
  document.CALC.mm.value="";
  document.CALC.inches.value="";
  document.CALC.touchedlast.value="";
  return
 }else{
  alert("The value you are trying to calculate is invalid.  nPlease try again.");
 }
}
 
function frmtNumber(expression,NumDigitsAfterDecimal){
 var strNum = new String(expression)
 var re = ".";
 var intDec = strNum.indexOf(re)
 if(intDec>0){
  intDec = (parseInt(intDec)+(NumDigitsAfterDecimal+1))
  strNum = strNum.substr(0,intDec)
  return strNum
 }else{
  return strNum
 }
}
function WhosLast(fld){
 document.CALC.touchedlast.value=fld;
}
function CtoF(tmp){
 var intTemp=tmp;
 intTemp=(intTemp*9);
 intTemp=(intTemp/5);
 intTemp=(intTemp+32);
 document.CALC.fahrenheit.value=frmtNumber(intTemp,1);
}
 
function FtoC(tmp){
 var intTemp=tmp;
 intTemp=(intTemp-32);
 intTemp=(intTemp/9);
 intTemp=(intTemp*5);
 document.CALC.celsius.value=frmtNumber(intTemp,1);
}
 
function ItoM(len){
 var intLength=len
 if(intLength.length>0){
  intLength=(intLength*25.38);
  document.CALC.mm.value=frmtNumber(intLength,2);
 }
}
 
function MtoI(len){
 var intLength=len
 if(intLength.length>0){
  intLength=(intLength/25.38);
  document.CALC.inches.value=frmtNumber(intLength,2);
 }
}
</SCRIPT>

<TITLE>Celsius/Fahrenheit Temperature Calculator</TITLE>
</HEAD>
 
<BODY bgcolor="#CCCC99">
<FORM NAME="CALC">
 
 <TABLE BORDER="0" CELLPADDING="5" CELLSPACING="0" WIDTH="270" bgcolor="#CCCC99">
   <TR>
     <TD HEIGHT="22">  
       <table width="204" border="1" cellspacing="0" cellpadding="0" bordercolor="#FFFFCC" background="../images/bg.gif" align="center">
         <tr>  
           <td class="t7" height="25" width="100%" nowrap>  
             <div align="center"><font face="Verdana, Arial, Helvetica, sans-serif" size="2" color="#FFFFFF">&nbsp;<font face="Arial, Helvetica, sans-serif"><b>Celsius/Farenheit  
               Calculator</b></font></font> </div>
           </td>
         </tr>
       </table>
     </TD>
   </TR>
 <TR>
     <TD>
       <table width="100%" border="0" cellspacing="0" cellpadding="5">
         <tr>
           <td><font face="Verdana, Arial, Helvetica, sans-serif" size="2">Enter  
             either value and press the calculate button.</font></td>
         </tr>
       </table>
       
     </TD>
   </TR>
 <TR>
     <TD align="right"><b><font face="Verdana, Arial, Helvetica, sans-serif" size="2">Celsius</font></b>  
       <input type="text" name="celsius" size="15" onchange="WhosLast('celsius');"></TD></TR>
 <TR>
     <TD align="right"><b><font face="Verdana, Arial, Helvetica, sans-serif" size="2">Fahrenheit</font></b>  
       <input type="text" name="fahrenheit" size="15" onchange="WhosLast('fahrenheit');"></TD></TR>
 <TR><TD align="center"><br><input type="button" name="calculate" onclick="Calculate('temp');" value="Calculate">
       <input type="reset" name="reset" onClick="touchedlast.value='';" value="Reset">
     </TD>
   </TR>
 <TR>
     <TD align="center"><A HREF="#" onclick="window.close();"><font face="Arial, Helvetica, sans-serif" size="2"><b>close  
       this window</b></font></A>  
       <input type="hidden" name="touchedlast" value=""></TD></TR>
 </TABLE>
</FORM>

</BODY>
</HTML>