Merging Data

Hi Everyone

I need to combine two sets of data (File A and File B). The structure is as 
follows (snippet):

FILE A:
<supplements>
<supp>
        <supp-desc>Half Board</supp-desc>
        <supp-price>£10</supp-price>
</supp>
<supp>
        <supp-desc>All Inclusive</supp-desc>
        <supp-price>£20</supp-price>
</supp>
<supp>
        <supp-desc>Sea View</supp-desc>
        <supp-price>£3</supp-price>
</supp>
...
</supplements>

FILE B:
<supplements>
<supp>
        <supp-desc>Half Board</supp-desc>
        <supp-price>£20</supp-price>
</supp>
<supp>
        <supp-desc>All Inclusive</supp-desc>
        <supp-price>£40</supp-price>
</supp>
<supp>
        <supp-desc>Balcony</supp-desc>
        <supp-price>£5</supp-price>
</supp>
...
</supplements>

REQUIRED OUTPUT:
<supplements>
<supp>
        <supp-desc>Half Board</supp-desc>
        <supp-price source="filea">£10</supp-price>
        <supp-price source="fileb">£20</supp-price>
</supp>
<supp>
        <supp-desc>All Inclusive</supp-desc>
        <supp-price source="filea">£20</supp-price>
        <supp-price source="fileb">£40</supp-price>
</supp>
<supp>
        <supp-desc>Sea View</supp-desc>
        <supp-price source="filea">£3</supp-price>
        <supp-price source="fileb">-</supp-price></supp>
<supp>
        <supp-desc>Balcony</supp-desc>
        <supp-price source="filea">-</supp-price>
        <supp-price source="fileb">£5</supp-price></supp>
...
</supplements>

DESCRIPTION:
I need to compare <supp> nodes based on the text value of <supp-desc>. If the 
<supp> exists in both files then the <supp-price> node from File B is added 
underneath the <supp-price> node from File A (a "source" attribute is also 
added). If the <supp> exists in one file but not the other, a <supp-price> node 
with the text value of "-" is added. "Sea View" and "Balcony" are examples of 
<supp> being present in one file only.

Any suggestions on how best to achieve the desired result will be greatly 
appreciated.

 
--
Kevin Bird