RewriteEngine On
# Well since the second rewritecond is only looking for
# for html files in the request, you don't need the first
# rewritecond and so it's commented. If you wanted to grab
# everything, then you'd need to uncomment the first 
# rewritecond so you don't infinite loop on the redirection.
#RewriteCond %{REQUEST_URI} !somescript.php
RewriteCond %{REQUEST_URI} ^(.*?/)*(.*\.html)$
RewriteRule ^ /somescript.php?page=%1 [L,R=301]