I have offline PC with any Internet access (inside private intranet), and I need set to buildr on this box.
Is it possible to make buildr installation on machine without access to the Internet?
Sure. You will need to collect the gems Buildr depends and all their dependencies, then download them from rubygems.org. You will then be able to install buildr by typing:
gem install buildr-1.4.7.gem
Here is a complete answer for an other gem, rails, the last answer seems to be on spot:
gem fetch rails -y -t /path/to/flash_drive