Input interrupt pin associated with TIMER1 on ATmega168
Does the code above determine which pin will provide the frequency to be measured? How?


No. Timer 1 is always clocked externally on T1, which is on PD5 on the 'XX8. If timer 0 was used instead then the external pin would be T0 (PD4), and so on. Setting CSn[2:1] to 0b11 merely selects the external input, and CSn0 selects the edge.


  Would that same code define the same input interrupt pin on an ATmega328?


The '168 and '328 have the same peripherals and pinout, only the memory differs (hence the "8" at the end, with the varying powers of 2). But no pin directly triggers the interrupt; it is triggered from the timer, which is clocked via PD5.