The custom content like modified WinPE goes in a separate place (along with backup copies of things like the GSS server's database and things like that), and this is related to how upgrades work in our installed (so it most respects, uninstalling and reinstalling a different version carries still forward a lot of state - normally that's the right thing to do).
All the content related to the Ghost Boot Wizard and the drivers and operating system images that it uses lives in the Windows document directory for "All users" - specifically for 2000/XP/2003 it will be found in "C:\Documents and Settings\All Users\Application Data\Symantec\Ghost\Template" - there's an equivalent location for Vista under Vista's user folder, and of course for non-English installs of Windows the directory is the localized equivalent.
Most of the content in that level is DOS drivers; the primary Windows PE image lives under that directory in "common\winpe" and the Windows drivers added to the DeployAnywhere database live in "common\windrivers"
[ If you go browsing for this directory, Windows has the "Application Data" folder hidden by default, so be sure to have browsing hidden folders on - or, cutting and pasting the above path into the Windows Start menu can take you there despite it being hidden. ]