Open Source - Excel to XML Converter

I am looking for an easy way to create an XML data
file. 

For example I have my xml data structure like this:

<books>

<book>
<isbn>1234</isbn>
<title></title>
</book>

<book>
<isbn>1234</isbn>
<title></title>
</book>

<book>
<isbn>1234</isbn>
<title></title>
</book>

</books>

It's a bit tedious to create this file manually and
was looking to enter the data in an Excel spread sheet
and then use a converter to convert from Excel to XML.

Does any one know a good converter?

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