It seems to me that this is a situation of "Owner Preferences". I would suggest that you select the Previous System folder, get information on it, open the tab for Owner Privileges, change the "ownership" of the folder to YOURSELF as the administrator, close the Get Info window, and then select the folder and move it to the trash. If that doesn't work, then you should boot to OS-9, open your OS-X drive folder, select the previous system folder and move it to the trash. Either way, you get rid of the space hog.