C: Drive has 400+ GB available on it
I rebooted multiple times and always closed everything (including AV) before starting
After a while I gave up and just played a bit (Recklessly, not worrying since I couldn't save)
Then, about a half hour of playing I accidentally hit the Quick Save button and it worked! Been able to save fine now since them
[Sequence. Started playing, quick saved, normal saved, quick saved... then all saves became corrupt as they saved, tried for about 15 minutes, saves always failed... after a half hour of playing without saving, I could suddenly quick/normal save as often as I want and load as often as I want...]
No idea

Working for now at least! It's a pretty fun game too!
Edit: Oh and it is a fairly recent install of Vista too. 2 months old, pretty clean, very little running on it. Maybe something to do with the HDD? However I have no issues with anything else, got steam installed and 3 or 4 steam games work fine