Alternatively, are there any open-source Stackoverflow/HN look-alikes that I can download and modify for my needs?There are multiple open-source clones of StackOverflow. One well-known and popular one is OSQA[1].
Additionally, the Reddit source-code is open[2] (although their license is one of the "weird" ones by my standard), so that's an option.
Also, I'm working on a project that is very reddit-like in a lot of ways, including the ability to vote things up/down, rank by votes, add comments, etc. It's still pretty alpha, but if you want to take a look see the source[3] and/or the demo site[4].
[1]: http://www.osqa.net/
[2]: http://code.reddit.com/
[3]: https://github.com/fogbeam/Neddick
[4]: http://spdemo.fogbeam.org:8080/neddick1
If you're interested in the Neddick stuff at all, feel free to shoot me an email. It's under active development, but the roadmap right now is entirely driven for my vision for the stuff I'm doing... I'd love to hear from anybody else that might be able to put it to use.
Edit: Oh yeah, almost forgot... the code for Hacker News itself is also available[5].
[5]: http://ycombinator.com/arc/arc2.tar