This is so simple to do. I just added a new Webmail. I didn't like Horde, and Squirrel just seems to plain.
I looked and found Roundcube. This looks real nice and so far its' running smooth..
Heres the steps I took to install it.
Logged into my WHM, Then set a Master database password (remember this)
Logged into SSH with putty and followed that tutorial. To install RoundCube.
Then found the email wouldn't send.
I found and made this change.
Look in /usr/local/cpanel/base/roundcube/skins/default/templates/compose.html at about line 31 and change the action from:
This change seems to allow the email to be sent.
Once that was done, Roundcube comes up with Horde and Squirrel mail.