Redmine

This seems to be caused by issues with the used howto's since they describe different ways of deployment mixed through each other even on multiple platforms.
For example: HowTo_install_Redmine_on_CentOS_5 tells you to install Phusion Passenger (the easiest way to deploy Rails/Rack apps) but it doesn't utilize it. Instead, it directs you to HowTo_configure_Apache_to_run_Redmine which describes generic deployment on:

• CentOS 5 with mod_cgi, mod_fcgid (multiple distributions) and mod_fastcgi
• Ubuntu Server with Phusion Passenger
• FreeBSD with mod_fastcgi

Regarding your situation: I'd suggest to choose Passenger as the way to deploy Redmine unless you have specific needs for the others. You should have installed it already as the CentOS 5 howto instructs you to do that.
Now, revert the changes you've made for HowTo_install_Redmine_on_CentOS_5 under:

• Rename dispatch CGI files
• Edit .htaccess file for CGI dispatch configuration
• Chown and Chmod files for read/write access for the Apache user

and revert the changes you've made according to HowTo_configure_Apache_to_run_Redmine (you haven't told what parts of the howto you've followed, so I can't give you precise steps here).
After this, deploy Redmine through Passenger (this is described in depth in the outstanding documentation of Passenger), and restart Apache/Passenger as the docs tells you to do.

Hope this helps as this is kinda hard to troubleshoot with the available information...