James:
If you use a ready made device called an oscillator then you can buss its output to the X1 pin on multiple processors. However I would only do this if all the processors were on one circuit board.

You mentioned the desire to use multiple microcontrollers and if this means using them in a distributed manner on various circuit boards then you should us a separate frequency source for each microcontroller.

You may find it overall easier to utilize a single higher end microcontroller to do the whole job in one chip. Check out the Silicon Labs processors. (can access info at the Silicon Labs Web site) They have some with eight ports of I/O (64 pins !!), 12 bit A/D, 12 bit D/A, many timers, dual UART, big FLASH and even up to 8K bytes on-board.

Michael Karas