Resistors and caps for PIC crystal oscillators:

In XT mode, I would use a pair of 20pF caps to ground and no series resistance.

In HS, I would use the same caps and a 120 or 150 ohm series resistor.  Check
the signal on a 'scope.  If you see big Vdd and Vss over (and under) shoots, you
need a bigger resistor.  If the signal is too small, less than 1 volt RMS, say,
your resistor is too big.  Generally, you will need smaller resistors at higher
frequencies.  Don't take this too seriously, if you use 120 ohms all the time,
you'll probably do fine.

- Mark Sullivan -