The hanging and freezing used to happen to me all the time - but not so often now, since I read a post here from someone who suggested downloading 'End it All' and 'Rambooster' (both of which are free - I'd give you the URLS if I could remember them, but I found both bits of software easily with a google search on their names). I have more RAM than you, but it might still help - run End it All first, and then Rambooster, and see if it does any good. The difference it's made to me and what I can render without a crash (even hi-res textures, which I never could before!) is amazing! But you really do need more RAM... (not that I'm an expert in these things!)