If you're using lastest Ubuntu 8.04, you may install ebox-mail package but it will override your postfix configuration to work with courier instead of using dovecot. LAMP installation is not modified at all. Take into account to change the eBox administration listening port from 443 if you're using that port in your apache2 installation (It will be asked in the installation process).
If you're using Debian Sarge, the same as above but apache 1.3 is used instead of apache 2.
Hope this helps.