Thanks peekay123, I thought that was the case, but I was getting a compile error that was making me think differently. What I'm working on is very similar to a thread you participated in back in march
At that point, the IntervalTimer library did not exist. I am not using the power switch tail, but the AC Dimmer Circuit by Robert Twomey.
I've been successful using his example code on the arduino. Granted, his code uses TimerOne. So, I've been trying my hand at modifying that code with the IntervalTimer,but am getting the following error:
"ac_dimmer_3.cpp:19:51: fatal error: SparkIntervalTimer/SparkIntervalTimer.h: No such file or directory
void zero_cross_detect();"
I''m guessing this isn't going to be as plug and play as I was hoping 
My modified code below. Thanks again
/*
AC Light Control
Updated by Robert Twomey <rtwomey@u.washington.edu>
Changed zero-crossing detection to look for RISING edge rather
than falling. (originally it was only chopping the negative half
of the AC wave form).
Also changed the dim_check() to turn on the Triac, leaving it on
until the zero_cross_detect() turn's it off.
Adapted from sketch by Ryan McLaughlin <ryanjmclaughlin@gmail.com>
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1230333861/30
*/
//#include <TimerOne.h> // Avaiable from http://www.arduino.cc/playground/Code/Timer1
#include "SparkIntervalTimer/SparkIntervalTimer.h"
IntervalTimer myTimer;
void dim_check(void);
volatile int i=0; // Variable to use as a counter
volatile boolean zero_cross=0; // Boolean to store a "switch" to tell us if we have crossed zero
const uint8_t AC_pin = D5; // Output to Opto Triac
int dim = 0; // Dimming level (0-128) 0 = on, 128 = 0ff
int inc=1; // counting up or down, 1=up, -1=down
//int freqStep = 65; // This is the delay-per-brightness step in microseconds.
// It is calculated based on the frequency of your voltage supply (50Hz or 60Hz)
// and the number of brightness steps you want.
//
// The only tricky part is that the chopper circuit chops the AC wave twice per
// cycle, once on the positive half and once at the negative half. This meeans
// the chopping happens at 120Hz for a 60Hz supply or 100Hz for a 50Hz supply.
// To calculate freqStep you divide the length of one full half-wave of the power
// cycle (in microseconds) by the number of brightness steps.
//
// (1000000 uS / 120 Hz) / 128 brightness steps = 65 uS / brightness step
//
// 1000000 us / 120 Hz = 8333 uS, length of one half-wave.
void setup() { // Begin setup
pinMode(AC_pin, OUTPUT); // Set the Triac pin as output
attachInterrupt(D1, zero_cross_detect, RISING); // Attach an Interupt to Pin 2 (interupt 0) for Zero Cross Detection
myTimer.begin(dim_check, 65, uSec);
//Timer1.initialize(freqStep); // Initialize TimerOne library for the freq we need
//Timer1.attachInterrupt(dim_check, freqStep);
// Use the TimerOne Library to attach an interrupt
// to the function we use to check to see if it is
// the right time to fire the triac. This function
// will now run every freqStep in microseconds.
}
void zero_cross_detect() {
zero_cross = true; // set the boolean to true to tell our dimming function that a zero cross has occured
i=0;
digitalWrite(AC_pin, LOW); // turn off TRIAC (and AC)
}
// Turn on the TRIAC at the appropriate time
void dim_check() {
if(zero_cross == true) {
if(i>=dim) {
digitalWrite(AC_pin, HIGH); // turn on light
i=0; // reset time step counter
zero_cross = false; //reset zero cross detection
}
else {
i++; // increment time step counter
}
}
}
void loop() {
dim+=inc;
if((dim>=128) || (dim<=0))
inc*=-1;
delay(18);
}