Add this to your yum.conf :
[mozilla-seamonkey]
name=Mozilla SeaMonkey Releases
baseurl=http://ftp.mozilla.org/pub/mozilla.org/mozilla/yum/SeaMonkey/releases/1.6/redhat/1
Or add to /etc/sysconfig/rhn/sources (One line):
yum mozilla-seamonkey http://ftp.mozilla.org/pub/mozilla.org/mozilla/yum/SeaMonkey/releases/1.6/redhat/1
Using yum 'yum update mozilla' Using up2date 'up2date -u mozilla'
Cheers, Michael