For some reason, I can't seem to get the mod_rewrite enabled. I've put

Options +FollowSymLinks
RewriteEngine On

in my .htaccess and turned on mod_rewrite in the configuration of memht but it does not work. Am I doing something wrong?

website is: http://www.cmstester.com

If the modrewrite is enabled (check admin > phpinfo, the link is in the admin main) then probably your site is contained in a subfolder different than public_html

sorry I don't understand what you mean.

maby set modrewritebase to /forum

Well... every shared hosting site is located in a folder named public_html (you can't always see it, but it exists). In some free and shared hosts, site files aren't located in public_html/* but in public_html/somefolder/*. This means that you have to indicate that somefolder/ in the .htaccess file as basepath, or he will continue looking for public_html/* instad of public_html/somefolder/*.

What's your absolute path? You can find it in your phpinfo