Unfortunately, I'm almost positive that it's a Toshiba problem. The way I understand it is that nvidia ships them reference boards and then they are free to modify them however they like. When I first bought my machine it had Windows XP installed and I went to download the latest drivers direct from nvidia and when I went to install, it said it couldn't find a valid nvidia card or something. If you look here: http://www.nvidia.com/object/winxp_2k_mobile_84.63.html
you'll see that Toshiba machines aren't supported by the nvidia driver. You have to download the driver direct from Toshiba. Basically, they have modified the boards that nvidia gave them in such a way to make the cooling mechanism non-standard and then written a BIOS hack/driver mod to make it work.
I've tried many things to figure out how to actually control the fan (including doing custom mods to the DSDT) but, DSDT code is pretty cryptic and the only thing I have actually accomplished is to once cause my machine to white screen shortly after bootup and stay that way until I removed the battery for half an hour. To be honest, I'm pretty sure I understand what they are doing to control the fan but, after the white screen incident, I'm happy (and lucky enough) to just be able to keep the fan on low at all times (2.4 BIOS). If you want to risk it, open up the DSDT code and start looking at the areas of the code that refer to VTMP. I'm almost positive that's what's controlling the fan (just too scared to mess with it any more). You may also want to grab the code for an older BIOS and see what the diffs are (specifically with VTMP).