Hi there, I recommend eGroupware as it is pretty easy to install and this can be done in under an hour if you are patient and follow the instructions from the site carefully.
First of all go to the Sourceforge egroupware site and download the latest version in 'tar.gz' format from:
http://sourceforge.net/project/showfiles.php?group_id=78745&package_id=79971&release_id=320768Then go here to download the latest version of the Install and Security Guide:
https://sourceforge.net/project/showfiles.php?group_id=135305&package_id=148522You may also wish to run Stefan24's excellent upgrade script for SME 6.0.1-01 from:
http://no.longer.valid/phpwiki/index.php/SME6.0.1ContribsThe above gives you more recent versions of several key packages and is easy to install but take care to read Stefan's advice before running this.
Lastly, if you go to Snoopyski's pages and download his 'Howto Egroupware' pdf guide this will make it much simpler. I would still read the official 'Install and Security Guide' first though.
See how you go with this. I am no expert on it myself but it must be easy to install as I did it even with my limited Linux knowledge!
Good Luck!