<IfModule mod_rewrite.c>
RewriteEngine On
RewriteRule ^(.*).html$ $1.php
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}.php -f
RewriteRule ^(.*)$ $1.php
RewriteRule ^users/(.*)$ info/profile.php?nick=$1 [L,QSA]
RewriteRule ^seller/([0-9]+)$ market/incfiles/usinf.php?id=$1 [L,QSA]
RewriteRule ^forum/thema([0-9]+)/?$ forum/viewtopic.php?id=$1 [L,QSA]
RewriteRule ^viewforum/thema([0-9]+)/?$ forum/viewtopic.php?id=$1 [L,QSA]

</IfModule> так попробуй