Hi David,
It looks like you're trying to capture the rising and falling edge of a signal that is 50 or 60Hz. The register settings you posted look correct for that (assuming Touch- is actually TACTL).
Are you asking how to pass the external signal into the TimerA module?
With the register settings above, the timer will use module input CCI0A as the capture trigger. The table on page 17 of the MSP430F2012 data shows that CCI0A is TA0, and TA0 is multiplexed with digital IO P1.1. Page 43 shows that setting bit 1 of P1SEL and ensuring bit 1 is clear in P1DIR and ADC10AE* will select the CCI0A function on that pin.
Hope that helps,
Rob
* This is the default on startup