For the most part, the installation happens in the target operating system, not in WinPE. So the real question I have is what is the goal here? Are you looking to install the AClient or DAgent (what is required to report into the DS console)?
If so, you can push it from the console by using the "Remote Install" menu option. Or you can install it via login scripts or manually by running the setup (located in \\servername\express\agents\aclient folder).
Just a note though, (a personal recommendation and not the official Symantec way), if you are running this on any windows operating system prior to Vista or 2008, use the AClient, it will save you a ton of headaches. If you are running Vista or 2008, then you have no choice but to use the DAgent.
Hope this helps.