RewriteEngine On
Options +FollowSymLinks -Multiviews

#Index
RewriteRule ^index\.html$ index.php [QSA,L]
RewriteRule ^([0-9]+)\.html$ index.php?CategoryID=$1 [QSA,L]
RewriteRule ^([0-9]+)-([0-9]+)\.html$ index.php?CategoryID=$1&page=$2 [QSA,L]
RewriteRule ^index-([0-9]+)\.html$ index.php?page=$1 [QSA,L]
RewriteRule ^index-([0-9]+)-([0-9]+)\.html$ index.php?CategoryID=$1&page=$2 [QSA,L]

#Categories
RewriteRule ^categories\.html$ categories.php [QSA,L]

#Extensions
RewriteRule ^extension\.html$ extension.php [QSA,L]

#Comments
RewriteRule ^thread-([0-9]+)\.html$ comments.php?DiscussionID=$1 [QSA,L]
RewriteRule ^thread-([0-9]+)-([0-9]+)\.html$ comments.php?DiscussionID=$1&page=$2 [QSA,L]

#Search
RewriteRule ^search\.html$ search.php [QSA,L]
RewriteRule ^search-([0-9]+)\.html$ search.php?page=$1 [QSA,L]