The PNG image uses transparencies. If your browser can't handle that (supposedly MS Internet Explorer has that problem) you can look at the PNG with white background or the transparent GIF. The latter doesn't look that good, however, since GIF does not support an alpha channel.
The SVG is also available.
If you need different sizes of the logo, I encourage you to check out Inkscape, which I used to draw the logo. It can export drawings to PNGs of any dimension.
The original can be found on the D Programming Language website.
Marcel Martin, 2005-02-11
Addendum on January 2, 2011: I consider my work (the vectorization of the logo) to be in the public domain. As far as I am concerned, use the vectorization as you wish. (If you like, you can send me an email.) Note that you probably need to get permission to use the logo itself.