Want to use Cron and Calendar or when
 

Using Debian Lenny.

I'm looking at using either Calendar or when for a calendar. I
like them both. Is there any features that are preferable?

My question is can I pop ups with these when I have an appointment
due? I read in an article about Calendar that I could use Cron to
email output. What command would I give for this and where would I
find the mail; or is there a better way?

Thanks

You can use the xmessage command with a DISPLAY argument to popup a message
ex: