(I agree, btw, this is a pretty fundamental thing.)
That's the textbook example I've been using since we started this whole project... :(
There is a compatible set, but right now you have to follow fluent nhibernate down to see what its most recent version uses for NH and then what that version uses for castle.core. Last time I did this I used rubygems site to walk the dependency chain.
The pain has always been there. Now that we are seeing the pain in a different context (package mgmt) instead of just after going out and downloading things and then finding out we have incompatibilities, we can start to think of ways we can helping the community solve these issues.
"Be passionate in all you do"