How can I tell Mac OS X's Internet Connect not to disconnect after 15 minutes of being idle?

In the Network system preferences, select Internet Modem from the Show pop-up. Click the PPP Options button at the bottom of the window, and then either uncheck the Disconnect If Idle For 15 Minutes to your desired amount of time.

Title:
Ditch Mac OS X's language files

How to rid myself of hundreds of unneeded language files in Mac OS X?

Your best bet is to be proactive when installing Mac OS X by choosing the installer's Customize option and deselecting foreign languages you don't need. If you already installed Mac OS X and running Mac OS 10.2 (Jaguar), use Mike Bobich's free utility Delocalizer (http://software.bombich.com/local.html) to delete unwanted language files and free up disk space. Delocalizer doesn't officially support Mac OS 10.3 (Panther), although many Panther users report using the app successfully.

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Run Prescheduled Tasks

Mac OS X's Unix core contains basic maintenance tasks that automatically clean up old log and cache files. However, they're scheduled to run weekly in the middle of the night - and because your Mac is probably shut down at this specified time, they don't run. To run them manually, launch the Terminal (Applications>Utilities) and execute the following commands one at a time - you need your admin password to invoke the sudo command:

sudo periodic daily
sudo periodic weekly
sudo periodic monthly

If you've never run these before, don't freak out if your system seems suspended for several minutes - the task has finished when you see a prompt. When finished with all the three tasks, reboot your mac.

Title:
Repair Permissions

When file or application permissions get damaged, they can cause your Mac to run slowly, so repair them periodically - especially after installing new software. Open Disk Utility
( Applications > Utilities ) and choose a volume from the left panel. Click the First Aid tab and then click Verify Disk Permissions to see what needs fixing, if anything. If you spot troubles, click Repair Disk Permissions to fix them.

(Information taken from MacAddict - May 2004)