something ownerships can only be change with 'sudo' from the command line or if you are logged in as root. i recommend NOT changing file ownerships at random, the results could be pretty disasterous.
Mac OS X 10.2.x:
Boot from Install Disk 1 and select Disk Utility from the Installer menu. Click the Disk First Aid tab. Select your Hard Drive and click the Repair permissions button. Quit the installer. It will prompt you to restart.