Cannot install Xcode 3.2.6 on Snow Leopard
The installer quit with "The Installation Failed An unknown installation error occurred." A look at /var/log/install.log revelead the problem to be "The package “iPhoneSystemComponents.pkg” is untrusted. CSSMERR_TP_CERT_EXPIRED.
CSSMERR_TP_CERT_EXPIRED is the hint - the certificate is expired. Setting the OS X date to 2011 fixed the problem