xml string replace

anyone have an example of replacing strings within an xml file...in my case preferences.xml? My app communicates with the outside world thru xml...
<myInstaller>
<cpu>$userCPU</cpu>
<sn>$HdriveSN</sn>
<connection>$connectionSpeed</connection>
<currentIP>$IP</currentIP>
</myInstaller>

many thanks

i guess any of the multiple replace functions do the job.. check the archive!