[kh99]

You might be able to make your block/widget an iframe that loads your htm file. Another way would be to use a php type widget/block and include an external file, like:

ob_start();
include('something.htm');
$output = ob_get_contents();
ob_end_clean();

// forum block needs a return, widget doesn't (but it might work anyway)
return $output;

Remember that widgets and forum block content is cached so when you change your htm file you won't see the changes until the cache expires (unless you set cache time to 0. But it's probably good to leave it set to at least 1 minute if possible).