[support] D7 upgrade - change to filtered html text format

Our Drupal 6 website has been around for 2 years and all editors use unfiltered html text format. Now that we know better and are upgrading to Drupal 7 I'm hoping to switch to filtered html. Since pre-existing nodes were created using unfiltered html, users assigned to filtered html can no longer edit node bodies. We need to use the secure format, rather than switch back to unfiltered.

I've been experimenting with editing the signature_format field in the user table, but am not sure of the allowed values. I tried a '2' and 'filtered_html' and neither allowed the user to edit the node. Is there another way to go about this?

Thanks in advance for any pointers.