XML : Need some help to export some info from PHP to XML

I have some problems exporting some info from php to a .xml file. Can somebody help me out ? I need the output to look like this :

  <rates>  <item>  <from>PMUSD</from>  <to>BTC</to>  <in>VALUE FROM PHP</in>  <out>1</out>  <amount>VALUE FROM PHP</amount>  </item>  </rates>    

My current code is :

  <rates>  <item>  <from>PMUSD</from>  <to>BTC</to>  <in><?php echo getBTCExchangeCourse();?></in>  <out>1</out>  <amount><?php echo getBalance();?></amount>  </item>  </rates>    

Can somebody help me out to build this script ? Thanks