I'm having the same problem. Here is mine.

Warning: main(/home/chadneu/public_html/install/../conf/_config.php): failed to open stream: Permission denied in /home/chadneu/public_html/install/index.php on line 3

Fatal error: main(): Failed opening required '/home/chadneu/public_html/install/../conf/_config.php' (include_path='.:/usr/lib/php:/usr/local/lib/php') in /home/chadneu/public_html/install/index.php on line 3

Line 3 is: require_once( dirname(__FILE__).'/../conf/_config.php' );

What's wrong? I think it's the /../ that is causing it.

ChadNeu,
When I try to hit /conf/_config.php directly I get a permission denied error:

Hey xxx.xxx.xxx.xxx guess what? You don't have access, so you're denied. Go back.

Try relaxing those permissions and see if it works. All b2evolution files that aren't meant to be accessed directly already have protection built in, so you probably don't need this security measure, anyway.

I have _conf.php at 777 for the install, all install files and most of the /conf/ files are 777.

Something is causing that message that I quoted above. If it's not file permissions, then it's something else. I can't be sure that it's related to the error you're getting when you try to install, but I have a feeling that it is. If that's not a measure that you put in place, then talk to your web host and see if they know what is causing that.