I've never written anything for cron (or done any programming outside of Director Lingo or Flash ActionScript). I want to create a daily backup routine for my data files. Where is a good tutorial for general cron scripting?

And: would cron be the best tool to write scripts that (a) check file modification dates/times, (b) creates a .tar for all files modified in the last 24 hours and (c) sends me an email when my backup directory has reached 600MB, saying that it's time to burn a CD?

Or would that task list be better to do in another scripting environment with cron just running those scripts on a daily basis?

Thanks!

Cron can be used for all you mentioned.
Cron scripts are just normal Linux scripts. So what you neeed is a guide to bash/sh scripting. Look at www.linuxdoc.org. There you'll find HOWTOs concerning bash and advanced bash scripting.