Well, before exploring the esoteric, lol, you might want to download the 10.5.8
combo update. Sometimes, when flakey stuff happens, it's due to a glitch in the update process, especially if you used Software Update to get to 10.5.8. Download from
http://support.apple.com/kb/DL866. Repair permissions, apply combo update (it will take a little while), then repair permissions afterwards. Then do Software Update in the event anything else needs updating. This won't hurt anything, and it just might fix the problem.
Also, reset PRAM (instructions below) and PMU (see note reference below):
1. Shut down the computer.
2. Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
3. Turn on the computer.
4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
6. Release the keys.
PMU:
http://support.apple.com/kb/HT1431
Please report back after these actions.