To call your Map Network Drive function I need the Server name and Share name. Any suggestion how I can get that from the Standard user session?

From a Cmd prompt a NET USE lists all my network drive mappings i.e. P:=> \\MyServ\PeeShare
In theory, what you can try to do is to develop a "helper" tool with SetupBuilder ("asInvoker" manifested) that calls the NET USE command and writes the result to a text file. You call this "helper" tool from your elevated running installer with the "Launch non-elevated under UAC" option enabled to perform the operation in the context of the "original" Standard User. After that, read the resuling file from your installer and retrieve the information.

From an Elevated Admin Cmd the NET USE also lists all the standard user mappings, but they all have Status=Unvailable, i.e. I see "Unavailable P: => \\MyServ\PeeShare". Can I get to that info in SB?
Again in theory, call the NET USE command from your installer and write the result to a text file. Then use "Handle Text File Operation..." to retrieve the required information.

When I am running the install on the Destination Folder panel when I click the Change.... button the drive mappings from the standard session do show, but with a Red X that I'm sure indicates its unavailable. If I pick one of those Red X drives (my P then Windows magically maps it into the Admin account. How can I do that with SB? I.e. ask it to map into the Admin session the P: from the standard session?
You can't do this programmatically from an application.

HTH,
Friedrich