Ok, I start to install game. Installer tells "Not enough free space at C:|". It's okay, because I do not install anything except OS on C:\, so this logical disk is never big on my system.
I go "Options", select my D:\ with 20+ GB free... but stupid installer continue to say : "Not enough free space".
What's the deal, gentlemen? Please, repair your installer.

Contact Support. They're unlikely to see this here, and unless there's some permissions issue going on (are you running it as an administrator?) then I can't think of anything that would cause this.

Maybe the installer uses the Windows' temp folder while extracting files, which by default is on the c: drive?