Run a 5VDC 0.2A fan from a 24VDC 3.75A power supply - Help Needed
You can use some 5V 3-pin regulator in order to lower the voltage, but you will get (24V-5)*0.2A =  3.8W on the regulator (and only 1W on the fan) - this is pretty bad efficiency. The regulator will need heat sink. 

Another solution is to use high efficiency switching regulator, but it will make the design over-complex.

So, the best solution is to use 24V fan - it will provide needed function without any additional overhead.