I had previously submitted an AppleScript that started up Internet Sharing on a Mac, as it is will not remain on after restarts. The need remains in Panther, but the AppleScript needs to be different. I don't know if the UI Scripting Beta is still necessary, because I upgraded without a clean install. See the previous hint for more information about getting this script to work.
A pane was added to Panther verifying that you want to share your connection. This new script gets past that pane. Here is the new script:
tell application "System Preferences" activate end tell tell application "System Events" tell process "System Preferences" click menu item "Sharing" of menu "View" of menu bar 1 delay 10 tell window "Sharing" if (exists tab group 1) then tell tab group 1 click radio button "Internet" delay 1 click button "Start" delay 1 end tell end if if exists sheet 1 then tell sheet 1 click button "Start" end tell end if end tell end tell end tell ignoring application responses tell application "System Preferences" to quit end ignoringCut and paste the above into Script Editor. If you then save it as an application and set it in your startup items, you won't have to worry about doing it manually.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031018154841400