[NgtCrwlr]

This one fires every 20 minutes
0,20,40 * * * * /your/pathto/newnews.pl >/your/pathto/cron_usenet.log

This one does its work twice an hour
0,30 * * * * /your/pathto/newnews.pl >/your/pathto/cron_usenet.log

Do you see the idea here?
If you want it to run at 12 mins past the hour and then at 43, 47, and 52 minutes past the hour it would be
12,43,47,52 * * * * /your/pathto...

This part of the line
>/your/pathto/cron_usenet.log
saves the output to the the file cron_usenet.log
You can then download cron_usenet.log and see if everything worked properly. Name the file anything you want, just make sure the path is correct for your server.

I hope this helps.