Sophisticated Circuits offers an excellent utility called iDo Script Scheduler Lite which allows the launching of up to three AppleScripts at preset times, repeating times, etc. The full $25 version does all this and more, allowing you to schedule an unlimited number of events, plus the ability to trigger scripts by Hot Key and whenever the system is idle. Check them out at www.sophisticated.com.
This common question has best been answered repeatedly in the Macscripter BBS. Some of the most mentioned solutions are QuicKeys, CronniX, iCal, iBeeZz… Just take a look to your favorite place for software downloads (eg, MacUpdate or VersionTracker).
You can also create your own scheduler using a stay-open script with an idle handler (thought it won’t work if the computer is asleep):
global runAtTheseTimes
on run
set runAtTheseTimes to (current date) + 2 * hours
end run
on idle
if (current date) ââ?°¥ runAtTheseTimes then
display dialog "We are 2 hour running! Now quit!"
quit
end if
return 30 --> check every 30 seconds
end idle