I thought I mentioned it in the Video, but for Corel 11, there is a bug in the PNG exporter. You need to go to
www.corel.com and download CorelDRAW 11 SP1, and while your at it get CD SP2. That should fix the problem.
Also, if you need to you can get transparnacy by exporting as PSD insted, even without the patch. But get the patch its a must.