You want to enable Clean URLs in Drupal 6, but the Enable bullet is grayed-out? Just enable Apache rewrite module, and you can enable this feature.
Windows hosting (WampServer)
I’m using Wampserver, if you are using something different, find out yourselg 🙂 Left click the wampserver-icon in the system tray > Apache > Apache Modules, enable rewrite_module. You’re done!
Now browse in your Drupal website to Administer > Site configuration > Clean URLs. And enable the feature.
Done.
When creating content you’re able to choose an URL yourself:
Unix hosting
If you’re using Unix hosting, make sure your .htaccess file is present and the line “RewriteEngine on” is not comment-out.