I don't use Bliss anymore cause they released GameVision
This flash chat system doesn't work good with Joomla. I use a bridge between Joomla and SMF Forum (
http://www.joomlahacks.com/ ), this flash chat works well with SMF, and other forum systems.
So if you want it with the same users as Joomla, you need to have the same database for the forum and Joomla, then you install that chat script in the directory of your forum (http://"your_domain_name"/forum/chat ). During the installation the script will ask you if you want to associate it with an other one. then all your actual user and new ones could use it.
Sorry for my poor English.