The installer progress bar moves based on the number of files copied and not the number of bytes or running of post-install scripts. Therefore, when installing the NetBoot Server, the installer looks as though it has stopped when copying large Disk Copy image files.
The same is true when the Web Objects installer starts to run its post-installation scripts.
Let an installer run for 10 to 15 minutes before you restart the server computer or try to stop the installer.