Dian,
First I opened it in Photoshop and saved it as a .png but I don't think that step was necessary. Then I imported it into Corel Draw and selected convert to bitmap. Since it was already a bitmap I don't think that step was necessary either. From the bitmap menu I selected "Quick Trace" and Corel Draw gave me a warning stating the bitmap was too large. I clicked on "Reduce" in the pop-up box. Then I deleted the original and exported as a .dxf. That's it. I didn't need to change any settings.