fluffymonster - 6 weeks.. you'll be fine.
i usually find that practicing in from of the mirror or with a friend who is clueless about the area helps me a lot before conference presentations.... at least with the not being 'tongue tied...' or to put it in another way- managing to express what my research is about.
you could try that. .
deiseal -believe me, i totally know what you're talking about. even talking to my supervisor about my research takes a lot. imagine a whole viva! am planning to do lots of conference presentations, workshops, seminars etc from summer to be able to overcome this. i guess it's being told you're wrong all the time. after a while you just begin to expect it and therefore don't see the point of talking about you're research - my experience anyway