Software update hangs on OS X Snow Leopard - how can I fix it?

Whenever I try to do a software update on OS X Snow Leopard, it gets to the point where it says it needs to restart, goes to the spacey background, and then sits there indefinitely.

I've tried booting from the OS install disk and doing permissions and file repairs (which did find and supposedly fix problems), but it still hangs.

Now I'm trying to update from the command line using sudo softwareupdate -i -a. For maybe 10 minutes, it's been stuck at "Writing files..."

In a different terminal window, I ran tail -f /var/log/install.log to see what it's doing. There it has hung at this:

Patching System/Library/CoreServices/BluetoothUIServer.app/Contents/MacOS/BluetoothUIServer

Is there anything I can do to fix this other than a full wipe and reinstall?

Update

With verbose output (the -v flag in sudo softwareupdate -i -a -v), I could see the program's progress in terms of percentages. The higher it got, the slower it went. It was repeating 99% when I left it for the night. In the morning I found it had been repeating 100% for hours. Time to try something else.

Fixed

I was able to fix this problem by downloading and running the Mac OS X 10.6.8 Update Combo v1.1.

After this ran and I restarted, I was able to successfully run Software Update, from the command line or the GUI; it now tells me that there is no new software to install.

Before doing this, I did check for I/O errors as @SethNoble suggested, then run the utilities that @Stephen suggested. I did not find any problems, although I had previously run Disk Utility from my OS X install disk and repaired both permissions and files.

It sounds like maybe the hard drive could be having trouble. I would recommend running Smart Utility. If the smart status says that the hard drive is ok then try running Disk Warrior. Let me know if either of those things work. I had the same problem once, if your hard drive is badly fragmented it has trouble installing things.