If your Leopard (Mac OS X 10.5) system is unexpectedly sluggish, logging might be the culprit. Run Activity Monitor (Applications/Utilities/ folder), and click the CPU column twice to get it to show most to least activity. If syslogd is at the top of the list, there's a fix. Syslogd tracks informational messages produced by software and writes them to the asl.db, a file in your Unix /var/log/ directory. It's a known problem that syslogd can run amok. There's a fix: deleting the asl.db file.
Launch Terminal (from the same Utilities folder), and enter these commands exactly as written, entering your administrative password when prompted:
sudo launchctl stop com.apple.syslogd
sudo rm /var/log/asl.db
sudo launchctl start com.apple.syslogd
Your system should settle down to normal. For more information, follow the link.
From Glenn Fleishman