RewriteEngine on
RewriteBase /download/
RewriteRule file/(.*)/$ files.php?cat=$1  
RewriteRule detail/(.*)/$ details.php?file=$1
RewriteRule download/(.*)/$ download.php?file=$1
RewriteRule top/ index.php?cmd=top
RewriteRule all/ index.php?cmd=all
RewriteRule category/(.*)/$ files.php?cat=$1
RewriteRule child/(.*)/$ files.php?cat=$1
RewriteRule result/(.*)/$ details.php?file=$1

ORIGINAL which works but only with .htm

RewriteEngine on
RewriteBase /download/
RewriteRule file(.*)\.htm$ files.php?cat=$1
RewriteRule detail(.*)\.htm$ details.php?file=$1
RewriteRule download(.*)\.htm$ download.php?file=$1
RewriteRule top.htm index.php?cmd=top
RewriteRule all.htm index.php?cmd=all
RewriteRule category(.*)\.htm$ files.php?cat=$1
RewriteRule child(.*)\.htm$ files.php?cat=$1
RewriteRule result(.*)\.htm$ details.php?file=$1