I'm new to Nginx and having troubles with porting my mod_rewrite rules to Nginx rewrite. Can someone help?

[code]
RewriteEngine on

RewriteBase /

RewriteCond %forum/{REQUEST_FILENAME} !-f

RewriteRule ^forum([0-9]?)/(.*)\.gif$ http://blabla.com/img.php?nick=$2&sert=2$1 [L]
RewriteRule ^forum([0-9]?)([t]?[0-9]?)/(.*)\.gif$ http://blabla.com/img.php?nick=$3&sert=2$1&text=$2 [L]


RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f

RewriteRule (.*)$ index.php/$1 [QSA]
[/code]