I understand that the fan control problem relates to laptops rather
than desktops - probably due to power saving circuitry that Toshiba
use.

Interesting that the crashing is so intermittent too - have you
noticed it relating to particular programs run on the days it crashes
opposed to days it doesn't ? Still trying to get a handle on what's
going on here - bearing in mind that WinXP work fine on it. Did we
ever discuss graphics chipset ? Reason for asking is that older Intel
graphics is a known issue with all flavours of Linux, not just Ubuntu.