On Gentoo you can install the gdc compiler by setting the Useflag 'd':
flagedit sys-dev/gdc +d emerge -n gdc
I would like to suggest the D documentation to use a sans-serif font like Arial instead of a serif font to improve readability on screens.
Beware of PATH modification: After executing the 1-click installer for Windows I found my PATH setting was reduced to a single entry for "D". Fortunately I was able to retrieve my previous setting from the "Path" value located in the registry at "HKLM\SYSTEM\ControlSet002?\Control\Session Manager\Environment".