Old style img_assist tags don't display pictures and break WYSIWYG editing

I am upgrading an old site from drupal 4.6 to 6.13. Some of the pages have the old style fid=xx type image assist tags such as this one:

[img_assist|fid=34|thumb=0|alt=CCC: cottage2.gif]

These images are not displayed on the page and if you attempt to edit in WYSIWYG mode with TinyMCE, the entire page content comes up empty. If I go into a different editor mode and delete all the "img_assist" tags, then when I switch to WYSIWYG mode the page content is available for editing (minus the images).

I am not sure of the status of support for the old style tags, though a migration path would be nice, however, at the very least they should not break the editor.