My b2evolution Version: Not Entered

I'm trying to add blogs to several websites I'm putting online this weekend. After running b2evolution on WAMP, where I was able to make it work (except for mixed results with stub files to set friendly URLs), I went to put it on a server.

I created a new database on the server, unzipped a fresh install and uploaded it to server, which has up-to-date MySQL and PHP. I put it into a b2evolution folder in public_html, changed permissions as per install instructions, creating _base_config.php along the way. As recommended in one post to this forum, I also changed permissions of public_html to 755.

Went to URL/blogs/install, reached the install page. Clicked to call the install script. Here's what I get:

"Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, webmaster@shoproute30.com and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request."

The server logs show the same the two errors repeatedly:

"[Sun Sep 06 19:08:48 2009] [error] [client IP] File does not exist: /public_html/500.shtml, referer: http://www.shoproute30.com/blogs/install/";
and
"[Sun Sep 06 19:08:48 2009] [error] [client IP] SoftException in Application.cpp:601: Directory "public_html/blogs" is writeable by group, referer: http://www.shoproute30.com/blogs/install/";

Is this a problem I can resolve?