Advanced CCK for Drupal 6

You can use Mediawiki syntax. It is possible that not all formatting options are supported at the moment.
Links to other pages: [[Page Title]] or [[path/to/page|Title]].
External links: http://example.com or [http://example.com some link title].
Interwiki links: [[site:Page Title]].
You can use the following interwiki links: path, gdo, wp
Images are included with [[Image:name]]. (wikipedia help)