XML view/edit Help PLEASE

Question

I have a form with:
Text Box = txtdisplayName
Text Box = txtdonotdisturb
Button = btnUpdate

I have an XML File:
-How do I add code snippets to this forum?-
?xml version="1.0" encoding="UTF-8" standalone="yes"?
phone1
reg
reg.1.displayName="NAME OF COMPANY"
reg.1.address="1234567" reg.1.label="COMPANY" reg.1.type="private" reg.1.thirdPartyName="" reg.1.auth.userId="1234567" reg.1.auth.password="PASSWORD" reg.1.server.1.address="IP ADDRESS" reg.1.server.1.port="5060" reg.1.server.1.transport="" reg.1.server.1.expires="3600" reg.1.server.1.register="" reg.1.server.1.retryTimeOut="500" reg.1.server.1.retryMaxCount="10" reg.1.server.1.expires.lineSeize="" reg.1.acd-login-logout="0" reg.1.acd-agent-available="0" reg.2.displayName="" reg.2.address="" reg.2.label="" reg.2.type="shared" reg.2.thirdPartyName="" reg.2.auth.userId="" reg.2.auth.password="" reg.2.server.1.address="64.78.230.84" reg.2.server.1.port="5060" reg.2.server.1.transport="" reg.2.server.1.expires="3600" reg.2.server.1.register="" reg.2.server.1.retryTimeOut="500" reg.2.server.1.retryMaxCount="10" reg.2.server.1.expires.lineSeize="" reg.2.acd-login-logout="0" reg.2.acd-agent-available="0" reg.3.displayName="" reg.3.address="" reg.3.label="" reg.3.type="shared" reg.3.thirdPartyName="" reg.3.auth.userId="" reg.3.auth.password="" reg.3.server.1.address="64.78.230.84" reg.3.server.1.port="5060" reg.3.server.1.transport="" reg.3.server.1.expires="3600" reg.3.server.1.register="" reg.3.server.1.retryTimeOut="500" reg.3.server.1.retryMaxCount="10" reg.3.server.1.expires.lineSeize="" reg.3.acd-login-logout="0" reg.3.acd-agent-available="0" />

call>
donotdisturb call.donotdisturb.perReg="0"/>
/call>
/phone1>

I want to:
On page load. Load txtdisplayName with the value that is at phone1/regreg.1.displayName
Load txtdisplayName with the value that is at phone1/call/donotdisturb/call.donotdisturb.perReg
Then on btnUpdate...Save the updated values in the text boxes BACK to the XML file to appropriate locations.
HOW THE HECK DO I DO THIS?
HELP PLEASE, Tom