First of all, the AppleScript. I placed it in the Library/Application Support/iSync directory, and named it SyncNow.scpt:
tell application "Finder"
set iSyncRunning to ¬
(number of items in (processes whose name is "iSync")
is greater than 0)
tell application "iSync" to synchronize
tell application "iSync"
repeat while (syncing is true)
end repeat
if iSyncRunning is not true then
quit
end if
end tell
end tell
Then add this entry to your crontab (edit in Terminal with crontab -e):
0 */2 * * * osascript Library/Application\ Support/iSync/SyncNow.scpt
This will sync every two hours; type :x to quit the text editor, and you are done.

