Create a .htaccess file and place it in your document root. and add the following
# don't allow anyone to view your htaccess file
ReWriteRule \.htaccess [F]
RewriteRule ^(.*)/(.*)/$ /index.php?archive=$1&bid=$2 [L]
In your index.php, do the following
$archive = $_GET['archive'];
That should do the trick.