For actionscript, it would be something like:
prefetch RoamingClient_MAC.pkg ????? prefetch stuff ????
folder create "/Library/Application Support/OpenDNS Roaming Client"
delete "/Library/Application Support/OpenDNS Roaming Client/OrgInfo.plist"
copy __Download/OrgInfo.plist "/Library/Application Support/OpenDNS Roaming Client/OrgInfo.plist"
wait /usr/sbin/installer -pkg __Download/RoamingClient_MAC.pkg -target /
But you would probably want to use a createfile command or similar to create the OrgInfo.plist… otherwise prefetch it. I can help with the createfile option if I know kind of what it looks like, but it should be mostly just copy and paste the contents of the file inside a createfile command.