go to menu
than go to C1 the one in orange than look for expanded sensitivity
go inside the expanded sensitivity and select "ON". Tada ur iso can go to 100
the base iso of the k-x is slated at iso200, but based on some tests that people have done, the base iso is probably iso125. i'm not really a very technical person, but what it means is that if you use the "expanded iso" function, you won't lose much DR as compared to what you get at iso200.
usually when you use "expanded iso", you will lose some amount of DR, as for most implementations, this involves the camera shooting at iso200, and then "dialing it down" a stop to achieve "iso 100", which is not true iso100. here, at least... based on what i've read, the problem is minimised.