If you have ever wondered, why none of the rdoc tasks in any rakefile 
ever work with your One Click Installer Ruby, here is the explanation.

c:\ruby\bin contains both 'rdoc' and 'rdoc.bat'. c:\ruby\bin is on the 
system path.

 From Windows point of view, rdoc is not an executable. rdoc.bat is an 
executable, but in its eternal struggle to protect the user from 
himself, Windows doesn't notice that. Hence:

irb(main):001:0> `rdoc`
Errno::ENOEXEC: Exec format error - rdoc
...
irb(main):002:0> `rdoc.bat`
... works...

Unfortunately system 'rdoc ...' is exactly what Rake does. Not sure 
where and how it can be dealt with. Can One Click Installer somehow cope 
with it? Or can Rake invoke rdoc.rb directly, rather than via an executable?

An ugly but effective workaround is to hack your local copy of 
lib/rake/rdoctask.rb, replacing sh %{rdoc -o  with sh %{rdoc.bat -o


P.S. I am fully aware of the common opinion that the _proper_ workaround 
is to ditch Windows. But circumstances force me :)

-- 
Best regards,

Alexey Verkhovsky

Ruby Forum: http://ruby-forum.org        (moderator)
RForum:     http://rforum.andreas-s.net  (co-author)
Instiki:    http://instiki.org           (maintainer)