add to xml data

[bhav69]

hi,
im creating a smart device application in vs.net2003 and i want to add new values to my xml file from the textboxes once i have clicked the 'add new button'.can anyone help please??
heres my xml file:

<?xml version="1.0" encoding="utf-8" ?>
<subjects xmlns="http://tempuri.org/states.xsd">

<subject name="Go to lab">
<task>Go to lab</task>
<StartDate>7/3/06</StartDate>
<StartTime>12.00pm</StartTime>
<comment>complete all task</comment>
</subject>
</subjects>

i want to add new subject in run time and it should save in the xml file

thanks..
bhav