Rewrite rule for nginx from Apache

[the_traveller]

First of all thank you very much mr Igor This is a great help for me
but as i'm new to nginx  so i'm little bit careful
but i have afew more things to ask about

do i have to make any defination to these params

SCRIPT_FILENAME
maindir

which is used as
fastcgi_param SCRIPT_FILENAME /path/to/script/pages.php;
AND
location /maindir/chat/

Or they just have to be written as they are??

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,23868,198889#msg-198889