Well, I downloaded the original Haven.jar that's linked to from Pacho's JNLP (which also seems to be about 150kb larger), and put it up on my own hosting and it seems to be running fine (apart from the fact that it can't connect because it's using the old Haven.jar as a base).
So I'm guessing that in order for a .jar file to load from a .jnlp, it has to be signed or otherwise edited in some way. I'm going to take a look myself, but I doubt I'll have much luck. Could maybe someone who's more familiar with java/editing jar files somehow patch Pacho's signed version of Haven.jar (http://hh-irc-extended-client.googlecod ... /haven.jar) with the newly updated haven.jar released by jorb (I have no idea where to find this but from reading this thread is sounds like some of you got a hold of it).
If someone could do this for me and get it working I'd be forever grateful. I know this should probably go in the Pacho thread since I'm using his JNLP version as a backbone, but it seems discussion here is more active and there have been a few recent posts by people who seem familiar with editing java/jar files.
For what it's worth I'm trying the workaround of getting the JNLP version to run correctly because I'm on OSX and can't seem to get any of the locally downloaded clients to run correctly, but that's a whole other mess.