This topic is about not being able to launch Bz at all, when having over 3GB of RAM. So your problem isn't slightly different, it is completely different.

(I'll split it when you read this.)
If you can save and exit, that means your Bz is not freezing, at least not completely. You must be experiencing Nvidia's yellow screen isssue. If you have the latest Nvidia driver there's no help for you beside waiting on a
1.5 patch which will fix those issues. In meantime, check Bz1.5beta installer available there.