Seems you are missing the following import in the docu.rb file (i am not a ruby expert, so I am guessing here:)):
require ‘albacore/config/docuconfig’

I added the above import and then things seems to work.

Untill i added the import I got the following error (full trace included):
PS C:\temp\ruby> rake –trace
(in C:/temp/ruby)
rake aborted!
uninitialized constant Configuration::Docu
C:/IronRuby/lib/ironruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2503:in `const_missing’
C:/IronRuby/lib/ironruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2503:in `const_missing’
C:/IronRuby/lib/ironruby/gems/1.8/gems/albacore-0.2.0.preview2/lib/albacore/docu.rb:6
C:/IronRuby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:30:in `require’
C:/IronRuby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:30:in `require’
C:/IronRuby/lib/ironruby/gems/1.8/gems/albacore-0.2.0.preview2/lib/albacore.rb:8
C:/IronRuby/lib/ironruby/gems/1.8/gems/albacore-0.2.0.preview2/lib/albacore.rb:8:in `each’
C:/IronRuby/lib/ironruby/gems/1.8/gems/albacore-0.2.0.preview2/lib/albacore.rb:8
C:/IronRuby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `require’
C:/IronRuby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `require’
C:/temp/ruby/rakefile.rb:3
C:/IronRuby/lib/ironruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2383:in `load’
C:/IronRuby/lib/ironruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2383:in `raw_load_rakefile’
C:/IronRuby/lib/ironruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2017:in `load_rakefile’
C:/IronRuby/lib/ironruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling’
C:/IronRuby/lib/ironruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2016:in `load_rakefile’
C:/IronRuby/lib/ironruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2000:in `run’
C:/IronRuby/lib/ironruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling’
C:/IronRuby/lib/ironruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:1998:in `run’
C:/IronRuby/lib/ironruby/gems/1.8/gems/rake-0.8.7/bin/rake:31
C:/IronRuby/bin/rake:19:in `load’
C:/IronRuby/bin/rake:19

Oop! that was my fault… remove the “v” in “v0.2.0.preview2″. it should say

gem ‘albacore’, ‘=0.2.0.preview2′

sorry about that – i’ll fix the post.

require ‘rubygems’
gem ‘albacore’, ‘=v0.2.0.preview2′
require ‘albacore’

I get the following error:
PS C:\temp\ruby> rake
(in C:/temp/ruby)
rake aborted!
Illformed requirement ["=v0.2.0.preview2"]
C:/temp/ruby/rakefile.rb:2

Any suggestions? I am using IronRuby.