Are you creating/editing the new files locally and then uploading/copying them to your server? This is the most dependable method. Editing on-site with Tiki's template and stylesheet editing features may not work, depending on the version.
Try making the simplest edit possible to your tiki.tpl, like just a row of XXXXXXXXXs or something at the top of the file, with no html tags. This should show up in the page in your theme. Or make an obvious change in your css file, like text size.
Also try clearing the site cache (at tiki-admin_system.php) and browser cache to make sure the most recent files are being used.
Normally theme file changes can be seen immediately.