Here is another way to edit the crontab file (not that theres anything wrong with the previous way!)
I like to write my crontabs out to a file, make a backup, edit the file, then write it back to the cron. I'm always careful of using crontab -e because if you do ^d in the middle of it, you wipe out the entire crontab. Yikes! And I've done that before.
So this is what I do:
crontab -l > crontab.username
# make a backup of the crontab
cp crontab.username crontab.username.MMDDYY##
vi crontab.username
# make my crontab edits
crontab crontab.username.out
# reads it back into the crontab.
Call that an abundance of caution. :-) Believe me, I've hosed my crontab on more than one occasion. And when you have crontabs that are like 3 pages long, that is NO fun.
backups are good. :-)