I know it's possible to connect two forums to one database, but I don't know where to change the table prefixes. This is phpBB, by the way. I'm using some kind of web hosting tools, so it didn't give me the opportunity to change the prefixes when I installed it. This is what I'm looking for: If a user registers at forum 1, they are automatically registered at forum 2.

If you can help out with anything, please post...It's much appreciated.

phpBB's installation specifically prompts you to enter a table prefix. You say you don't have that option with your host because they give you some single-click install or something? I don't know how to tell you to get around that. If you wanted to manually change the table prefix for a phpBB install, I'm sure you can. It most likely involves renaming all the tables and modifying a table prefix setting in a config file. I wouldn't want to try it on a board already in production, though.

To integrate auth between two completely seperate installations of phpBB, I don't know exactly because I've not done it, but there is documentation available that talks about how to integrate phpBB auth with other apps...so I'm sure you can hack it.

If the board communities are so similar to assume common logon, why not just use ONE board? Make the 2 main areas main categories of the one board. Members login, then go to the main category of their choosing. You can even have 2 domain names and depending on which the user visits, you automatically direct to the correct category of the board. I'm sure you have reasons to keep them totally seperate, though.