Good news is they worked on an Windows 2K3 environment for Siebel 7.8, so it may be worth talking to them. I realize that you are looking to conduct your own evaluation using open source - but in this case it may be worth talking to our services folks. The plugin we worked on was very specific to the use case for the company who deployed it, and was only developed essentially for one platform because of the way Siebel works. If you are serious about HQ working for you, they could help you flush that out probably in far quicker time than you could monkeying with it yourself.
Not trying to push you to spend $$, but it may be an option that could save you time, which in my book is always money 🙂