Figure out the Resistance Value With Known Device Specs
From the specs, I am assuming 5V is the voltage drop so V = 9-5 = 4. Plugging this into Ohms Law 4 = R*.2 So that would work out ot a resistor of 20 ohms. Is this right ?


200mA is the maximum current.  The minimum is zero (device off), so your voltage will vary between 9-(20*.2) = 5v and 9-(20*0) = 9V.  Since average current is usually a lot less than maximum, you'll mostly be giving the device too much voltage.

That might or might not be ok (most devices that use USB tend to be robust), but the best solutions here are to either get a 5v supply, or to get a voltage regulator (a device that takes one voltage and turns it into another).  A linear regulator such as the 7805 is the most simple, but will waste some battery life.