I just wanted to point out one more option for wrapping Ruby/Tk apps for shipping and installation onto other computers. That solution would be RubyGems. The following is a synopsis taken from the RubyGarden website:
RubyGems is a new approach to managing packages of Ruby code. The most convenient feature for the average user is that gems (apps and/or libs) can be downloaded and installed in one step from the command-line.
I haven't really looked into this technology that much yet, but it sounds just like what your looking for. If you want to find out more about RubyGems, you can do so at the RubyGems Wiki or you might want to look into the newest edition of the Programming Ruby book (Pickaxe II) from the Pragmatic Bookshelf where you'll find a chapter entitled "Package Management With RubyGems".
I hope that helps out, and thanks once more for the kind words. Oh, and be on the lookout for more Ruby articles in the near future.