Had some fun earlier today setting up an environment to use the drupal htmltidy module in in a Fedora Core environment. The README.txt file in the module was rather brief, but I needed to run the following to set it up on FC5:
yum install php-devel tidy libtidy-devel
pecl install tidy
php-devel is needed to run the phpize and tidy/libtidy-devel are needed to provide pecl with the libraries to incorporate these into php.