There is a brasilian (Rafael Steil) that develops a forum based on Java (http://www.jforum.net/). This is a great forum. Why dont you upgrade this forum to JForum? I dont know if you can export the database of this forum to JForum, but if it could be done i think it will be really great!
In the past we have gone through cycles of comparing features of various forum software, how easy it would be to migrate, what the support level would be like, how easy it would be for us to customize, and so on.
There are certain features that we consider indispensable. There are others that we might be willing to live without if we had the chance to add them ourselves later (or the creators of the software were willing to add them). And there are other features that we might be willing to live without if we consider them a tradeoff for getting some new features.
So far we have not found any alternative forum software that presented a compelling case for moving to any other existing forum software. And that is even without us worrying about the pain of converting from one forum format to another. Compound that with the fact that we know how well our current software works - for any other software we would need to perform stress testing and a phased roll out to ensure that it can handle the load that JavaRanch currently experiences.
(And we are not going to move to Java forum software just because it is Java - there has to be a more compelling reason than that)
We like to hear about forum software alternatives, but be aware that this is something we have looked at many times in the past, so it is likely that we may not spend a lot of effort looking at now.