The free demo has all MPEG functions removed due to license restrictions... I presume that includes calling Encore
You may export from the trial to AVI but not MPEG
My guess is that Encore CS3 will be required for this functionality to work.
As has been stated, the trial version has no MPEG capability, at all.
Now, you have the CS3 trial. So long as none of your Assets is MPEG, you can Export from the CS3 trail as DV-AVI Type II. I'd recommend doing this as elemental streams, i.e. Video to DV-AVI and Audio to PCM/WAV. These files can then be Imported to your EncoreDVD 2. Import the Vdieo (.AVI) as a Timeline and your Audio (.WAV), as an Asset. Drag the Audio from the Project Panel to the Timeline with your Vdieo. Author as desired, and Burn DVD.
PS surprised that you have a trial of CS3 at this late date. Luckily, you have EncoreDVD 2, to fully test CS3 with.