i don't know if this converter is created in javascript http://www.oanda.com/currency/converter/

i want to make like that but first i want to start on the combobox..
how to put a image in a option value in a combobox?

Making the converter can be done in JavaScript, like you showed on the link you added. I'il give you a head start on how to:

You have two text inputs, I already made the first for you:

The currency you have: <select id='have_cur_type' onchange='NewHaveCurType(this.value)'><option value='euro'>Euro</option><option value='dollar'>Dollar</option></select><br />
The amount you have: <input type='text' id='have_cur_amount' value='0' />
<br />
<br />
<input type='button' onclick='Convert()' value='Convert Currency' />

And then you have the javascript:

var have_cur_type = 'euro';
var need_cur_type = 'euro';

function NewHaveCurType(type) {
  have_cur_type = type;
}

function Convert() {
  
  var have_cur_amount = document.getElementById('have_cur_amount').value;
  // Also retrieve the other...
  
  // Now you need to calculate the ratio from one currency to the other, I would advise if you would first translate them all to one currency for example dollars and then translate those into the final currency the user wants

}

~G

Graphics
nice guide sir..how to put the answer to the currency i want amount textbox sir?