So I downloaded a bunch of updates from the Software Updater, a couple of which required a restart. One was a Mac OS 10.5 update. Now, on the installation screen at startup, with the progress bar and the words "configuring installation" below it, the screen is frozen. The bar hasn't moved in about an hour. Will restarting the computer do damage because it's in mid-installation?
I think there is a fair chance you'll have to do a fresh install if you reboot - formatting your hard drive and basically starting from scratch. My personal experience is that rebooting during an OS update won't "damage" your hardware, but might corrupt the boot sector forcing you to reinstall the OS and redo the update.
There is a chance the drive is bad (which *could* explain why it froze during the update), in which case, you're still in the same boat. At this point, there's only way to find out, and that is to reboot, so...
I would do the following:
1) Reboot and immediately boot to an installation disk (Hold Command and C with the OS disk in the drive)
2) Run Disk Utility from the Installation Disk upon reboot
3) Run Verify Disk on the harddrive
4) If everything checks out, reinstall the OS and redo the update
I think the biggest concern is that you have a bad hard drive, but I wouldn't worry about that until AFTER you Verify the Disk. AND DO REGULAR BACK UPS!!
I rebooted without the startup disk and it appears to be working like normal, though without the updates I downloaded. All the limited data that was on the drive is there and appears to be undamaged. There's an authorized Apple repair shop here in Cambodia — that's where I got the new HD put in — so I think I'll take it back to them to get it sorted out.
My girlfriend's parents gave me their old Mac Mini (with a dead hard drive) after declaring it surplus and deciding it would make for a nice plaything. It's one of the earlier models (A1103, if that helps), back when they were using PowerPC processors.