How to schedule an app to run?

Hi,
Can anybody tell me of an app that I can use to schedule when to launch an app or script?
Basically I want to display a dialog box with a message or a growl notification at a certain time monday to friday. I can make this notification as an automator script but I need a way to schedule when for it to run...

Thanks.

 

I guess the only problem is that it means I have an extra event clogging up my iCal every day, but I could always make its own calendar for it and hide it... I'll have a look...

Edit: Looks likes that works well for me. Cheers.