Making Forums Accessible

 
Hello Everybody,
 
I am building a website for a Charity for Disabled People. I am using joomla 1.5 and want to build a forum that is accessible. Unfortunately, I am having trouble in making the forum accessible.
 
I am also having trouble in preventing unregistered users from creating blog entries.
 
Could anyone please help me and guide me on these issues? I am grateful for any help.
 
Many Thanks,
Yasmin