This looks lik bug 48524 (Colin, please correct me if I'm wrong). This is fixed in dapper-updates, so you can work around it by upgrading all packages with 'ubiquity' in their names on the running live CD before starting the installer.
-- Installer crashed https://launchpad.net/bugs/57609 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
