my .htaccess file is not working

[eluser]zzet[/eluser]
1. question: Are you using PHP4 or PHP5?
2. question: Is your PHP running as a CGI or as an apache-module?

You can try these things:
RewriteRule ^(.*)$ /index.php/$1 [R] instead of ... [L]
or (if you have access to your php.ini and your PHP is running as CGI) you can add this line to your php.ini:
cgi.fix_pathinfo = 0