sounds to me like you dont really need a message board - it would be an incredibly inefficient way of storing the information that you mention and you'd find that people wouldnt use it too much as a result (IMHO).
Certainly what you'd need would be a database driven website, but just going for a simple message board wouldnt do the trick. You'd probably want to have a keyword registration system (for easy searching), salary ranges, locations etc. If you tried to do it with a message board then you'd be stumped by how to arrange things - a different thread for each country or county? Or a different thread for each subject? What about heads of departments etc?
I think you're going to have to go on a course (or at the very least buy a book) on either php or asp's (or any of the other variety's that are available), and then really plan to deploy a bespoke web application for it. I think if you aim to go down the freeware route you'll end up spending a lot of time trying to get it to work or do even half of what you want it to, and still wind up dissapointed at the result. What you're trying to achieve is quite a feat, and expecting the number of hits that you are it's going to be quite a task. I dont want to put you off, but I do think you need to be realistic if you're even thinking of over 1000 hits, let alone 15,000: that's a pretty busy site...
But good luck on whatever course of action you take!