DirectoryIndex sp_index.php

RewriteEngine On 

RewriteRule ^folder/([A-Za-z0-9_.!']+) sp_index.php?dir=./$1
RewriteRule ^file/([A-Za-z0-9_.!']+) sp_index.php?file=./$1
RewriteRule ^thumb/([A-Za-z0-9_.!']+) sp_getthumb.php?source=$1