How can I make 2 Drupal websites share the same user table so when a user is logged in on one they are automatically logged in on the other?
Your question seems to be all over the place. However, the Bakery Single Sign-On System module sounds like what you need.
Bakery provides a "single sign on" feature for Drupal based sites that are on the same second-level domain (i.e. example.com, subsite.example.com, subsite2.example.com). It could also provide support for any other website that implements the same web cookie, xmlrpc, and POST methods.
This module started at the 2009 Drupal.org redesign sprint in San Francisco as a way to manage single sign-ons across *.drupal.org infrastructure.
Read the bakery documentation for more information.
tl;dr Try using the Domain module suite. I allows you to run a site that "pretends" to be more than on domain, and helps you with relevant access rules and content sharing.
My experience with sharing tables is that you are in for a world of pain. I've tried it twice in the past and it has had various odd effects, due to various modules becoming confused. I no longer remember any specifics though, but if I did it today, I would take my own advice from above. :)