1. Make sure whatever directory you are installing to is running PHP5. See this page: http://faq.1and1.com/scripting_languages_supported/php/5.html for more information.
2. FTP all the files up to your 1and1 hosting directory. I went with version 1.7.3 available at http://elgg.org/download.php.
3. Create a 1and1 database for your Elgg installation.
4. Write down all your database information: username, password, database name, and host name.
5. [...] . . . → Read More: Installing Elgg on 1and1 Shared Hosting