Unfortunately with all Bethesda games, crashing is one of the inherent 'features'![]()
So after a bit of trawling a crapload of sites with reference's to fallout 3 crashes and freezes (a lot more specifically when entering houses/confinded areas), I found this.
http://www.tomshardware.co.uk/forum/page-100562_25_50.html
It's worked a charm for me almost immediately and that's even with reloading a crash save, I can't believe that after such a massive amount of time from release that this game still has so many crashes.