WOAH! DO NOT DO THAT!!
When you say large 4-pin, you are talking about these right:http://en.wikipedia.org/wiki/File:Molex_female_connector.jpg
And the small 4-pin looks like this:http://img.tomshardware.com/us/2007/08/09/pc_power_supplies/floppy-power.jpg
Yeah, those are all power cables.
That small connector on the end with 4-holes is a POWER port for a floppy drive. Your computer won't boot because you are probably shorting-out the motherboard and the power supply is going into a fail-safe mode.
If those are the only cables your fans connect with, then you cannot monitor them, they don't have the necessary sensors and connectors.