If you download the sourcecode for PHP from http://www.php.net/ (make sure to get the same version you are running) just change into the ext/cybercash directory, type "phpize", then "make" You should get a cybercash.so file, which you can copy into the same location as the other .so files. Then, add the line "extension=cybercash.so" to your php.ini file and restart apache.
You might want to create a php file that just has <? phpinfo() ?> in it and view it. It will tell you where those .so files go (it's the extension_dir line) and where your php.ini file is.
I don't use RedHat, so I haven't tried this myself, but it should work.