I run a decent system with Vista32 and I regularly run torrents with a scheduler at night.
I've been doing this for months, and the past 4 days my computer has encountered a "critical error" and rebooted. This happens usually within an hour of my torrents downloading.
I tried downloading during the day, and there was no reboot.
The shutdown has never occurred in front of me, I don't know the error. I also have enough power/hard drive space which could otherwise cause an error.