We're getting closer...
What are you trying to drive with this "very precise frequency"?
There are tools which let you examine the hex file that is uploaded to the arduino. I'm not sure of the exact name, but avrdump, or something like that comes to mind.
Serial printing in an ISR is going to cause problems. Serial data transfer is a slow process. ISRs need to be fast, so interrupts are not missed, while you're busy writing data out.
I'm the last person to tell you anything (else) about interrupts. If you start at the beginning, explaining what you want to accomplish, I'm sure others can offer suggestions.