Please download and install this "Windows Installer Cleanup" Utility from below URL:
http://support.microsoft.com/default.aspx?scid=kb;en-us;290301
After install please follow below steps:
1) Launch the utility.
2) Select Dimdim Publisher from the list.
3) Click Remove to uninstall the Dimdim Publisher
4) Go to "C:\Program Files\Dimdim\Publisher" and delete the content.
5) Go to http://webmeeting.dimdim.com/dimdim/ and install the new publisher.