Follow installation instructions.

Modify /etc/php.ini according to docs.
    Change session.save_path to a dir r/w only to apache owner.
    session.auto_start = 1
    session.bug_compat_42 = on
    max_execution_time = 600
    register_globals = On

Changes to at least some php.ini parameters require an Apache restart in
order to take effect.

Tell squirrelmail that your IMAP server is "other".  Do not choose "uw"
even if you are running Univ. Wash. because that causes a bug where 
SquirrelMail will only show you the messages in your Inbox.

Options / Display Pref / Num Msgs to Index  is actually no msgs displayed.
BUT WILL NOT CHANGE THE VALUE!!

BUG:  Is not displaying parent folders.  Sometimes incorrectly displays
 a different folder as the parent (which you can expand), sometimes 
 displays nothing.