Controlling the fanspeed for a MacBook under Linux is quite easy. For new kernels, smc support is built-in, so all you will need to do is issue the following command:

echo "4000" > /sys/devices/platform/applesmc.768/fan1_min

To monitor your system temperature, you can use a variery of applications. A good graphical tool in gnome is called "hardinfo", which will monitor, benchmark, and profile your system as a whole. Or, if you prefer a command line approach, you can install "lm-sensors". There are others, but these are the only two I ever really need to use.