Drupal Multi-Domain Single Sign On Project

We need true single sign on functionality across 14 or so domains presently functioning on Drupal 6 via Domain Access. We are open to suggestions of how to get it working so feel free to advise as necessary. Please visit our ELance project post in order to bid. This is a project we are looking to complete soon.

ELance Project

We have under development a network of sites which need to function as a single unit. We require a single sign on solution which will effectively and seamlessly allow a user to sign in/out of 1 site and have that be in effect throughout the rest of the network. We already have in place a shared user authentication table, so accounts need not be recreated on individual domains but this is not enough.

Our network of sites is presently being run on a Drupal 6 installation with a single code base and a single database (no table prefixing) and we would prefer this configuration remain if possible. We tried to implement several publicly available modules and all have, for varying reasons, failed. We desire a simple solution which will preserve our data and work thus far invested.