Both the GIF and PNG file formats support background transparency in Xara3D. Transparency makes background areas not covered by the Xara3D image transparent, so you see the web page background in these areas. Simply check the "Transparent" option in the Export dialog. This option is dimmed for BMP and JPEG since these formats do not support transparency.
Important Note: Xara3D anti-aliases the edge of a transparent bitmap to the Xara3D background color. For best results you should make the background color in Xara3D the same or similar to the color of the page the graphic will appear on, even when you are exporting as transparent.