RewriteEngine On
RewriteBase /www
RewriteRule ^/W/$ (index.php/Main_Page) [L,QSA]
RewriteRule ^/wiki$ (index.php?title=Main_Page) [QSA]
RewriteRule ^/wiki/$ (index.php?title=Main_Page) [QSA]
RewriteRule ^wiki/(.*)$ (index.php?title=$1) [QSA]

New:
RewriteEngine On
RewriteBase /
RewriteRule ^W/$ index.php/Main_Page [L,QSA]
RewriteRule ^wiki$ index.php?title=Main_Page [QSA]
RewriteRule ^wiki/$ index.php?title=Main_Page [QSA]
RewriteRule ^wiki/(.*)$ index.php?title=$1 [QSA]