If you are having trouble upgrading your Mac to Leopard, unplugging your external hard drives may be the simple fix you are looking for.
After I inserted my Leopard install disc and rebooted, my Mac froze up. I rebooted a few more times, and each time it chose my external backup USB drive as the startup disk and launched the Tiger setup routine. As you can imagine, this cause all sorts of problems. Long story short: avoid sharing my Leopard mini-headache by unplugging your external hard drive(s) before you reboot into the installer.
