Drupal Community Portal

I've decided to take on Drupal ... yesterday(!), therefore I'm at the installation level. I have experience with other CMSs and I would like to get a reliable link to a recent multisite installation guide/tutorial of Drupal for the 7.x version. I'm using Eclipse locally, my Apache 2.2 web server pointing to a virtual server already set-up in the workspace. I'm then uploading the sites to a shared hosted server where I can play with both virtual servers (subdomains) and main domain's subfolders. I want to make sure: that Drupal upgrades will not interfere with the sites folders and that I manage a 100% separation between the sites (I don't really care about having just one database, on the contrary).
Thanks