Something like this.
/path/to/public_html/.htaccess
Code:
RewriteEngine On
RewriteRule ^tutorials$ forum/forumdisplay.php?f=XX [NC,QSA]
You might have to alter that based on your physical base path and so on.
If you're using URL rewrites, it's a good idea to put forum data in a completely separate folder (e.g. public_html/forum_data) to your virtual paths (e.g. example.com/forums).