I have an XML files that contains grades in different subjects from
year 2005 =13 2007 .
In the HTML file I have several drop down list that contain all the
names of the subjects. If I select for example history from the first
one ,  I get the grade for 2005 in the first field, then the grade for
2006 in the field next to it and the grade for 2007 in the third
field.
Then I go to the second drop down list , select another subject name
and get all related grades in the proper fields.
So I have a page with approximately ten drop down list.

Now I have some fields in addition that presents calculated average.
For example ,  One is an average of all the subjects per specific year
and the other is an average of specific subject to years
2005-2007.These fields are changing dynamically as soon as I select a
value from the drop down list and related grades are being retrieved
from the xml file. How can I achieve this ?

this is a short example of the xml file. The real file contains about
10 subjects.
<summary>
<subject>
<name>history</name>
<grade in 2005>85</grade in 2005>
<grade in 2006>72</grade in 2006>
<grade in 2007>67</grade in 2007>
</subject>
<subject>
<name>chemistry</name>
<grade in 2005>75</grade in 2005>
<grade in 2006>62</grade in 2006>
<grade in 2007>97</grade in 2007>
</subject>
</summary>