Calculation of transfer function in OP-AMP circuits
Dimchtz - both currents (I1 and I2) meet at the inverting node. 


For the first circuit, you must therefore consider that I2 is the total current driven by output. With other words: The current through the parallel connection. That is what you have done - hence correct.  
For the second circuit, I2 is only the current through R (connected to the inv. input) which is to be used. My recommendation: use the voltage divider formula for finding the voltage Vx across R||C  - and as a next step you will find I2 by applying Ohms law for the resistor R (I2=Vx/R)