Possible, but you definatly need to know PERL and PHP.

Anything is possible in life... But in this case, not really. Joomla, has lots of scripts that will hand shake with it, and you would have to see if a plug for MediaWiki has been done... eblah (SQL) as far as I know does not have a plug for Joomla.

No, if it's for a company site or something, you might be able to hire a programmer to do it for you, but unless you really know what you're doing, you probably can't. It's not as simple as downloading something, thats for sure.

You could make this work. However, you would need to know how the Eblah table in the MySQL database is setup as compared to the Joomla table. I am not familiar with the structure of these, but I am sure that it would not be too hard to figure out. Look at the column headings for both the Eblah and Joomla table and research how you can link the two or combine them (if possible). Combining would only be possible if you could add new columns containing the data from Eblah with Joomla. You would also have to learn how Eblah and Joomla writes to their tables and modify them to write to the new columns that you combined. I know this may be a bit confusing, but you can look into this. I have not tested this procedure but if you are up to the challenge, you can give it a try.

MAKE SURE TO BACKUP YOUR DATA before you do anything with your MySQL tables. If you don't know what you are doing, don't do it. One wrong move could render your forum/Joomla CMS unusable. I am not saying this to scare you, but to make you aware of the risks of doing this.