A mac enthusiast friend has pointed me at this totally excellent utility. It’s a life saver if you have an OS X problem and don’t have your installer disk handy, because it can repair your disk for you from single user mode even with Tiger, with just a simple command. It will also repair permissions, and clean your caches and swap files while it’s at it.

Just type applejack auto restart at the command prompt and it will run, do its checks and repairs, and then reboot with the GUI for you.