Options +FollowSymlinks
RewriteEngine on
RewriteRule ^([a-z0-9_\-]*-(f|all)[0-9]+(p[0-9]+|/forum/index[0-9]*)?\.html)$ forumdisplay.php/$1 [QSA,L]
RewriteRule ^([a-z0-9_\-]*-(t|p)[0-9]+(p[0-9]+|/forum//index[0-9]*)?\.html)$ showthread.php/$1 [QSA,L]
RewriteCond %{REQUEST_URI} !(/forum/index\.php|\.css) [NC]
RewriteRule ^(archive|sitemap)/(.*)$ $1/forum//index.php/$2 [QSA,L]