I've been having the same thing happen (I'm running Windows 7 though). I found out that every time it freezes (mid-dialogue, mid-combat, even mid-load), I can wait for about 1 or 2 minutes and it suddenly starts up again. Have you tried just leaving it when it freezes, without pressing a key or clicking the mouse? I found it happens every hour or two, so it's worth the minute of downtime. Might be worth a shot...
If it does work, my only other piece of advice is to have two saves and alternate between them every time you save (or backup your autosave every half hour or so) because if it locks up mid-save, it doesn't continue loading and also deletes that particular save file.