Hi,
Thanks for doing the schematic pedja089 - that's exactly what I'm talking about. The 15k, 2k will give a low level of 0.39V. I looked at a 18F2420 datasheet and it states max voltage for a logic low on a schmitt trigger input to be 0.2Vdd or 0.66V with a 3.3V supply so you're below that by some margin - but not much. Definitely worth a try. Double check against correct datasheet!

but since that's in series it's position shouldn't matter.
Yes, I'd say it matters. You want the cap close to the PIC and the resistor close to the cap - not at the switch.
If you're trying to filter noise generated from the switch itself bouncing etc then it wouldn't matter but in this case you're trying to filter out noise being coupled into the wires. If you put the resistor far away from the capacitor (which you want close the actual input pin) the noise can be coupled into the part of the wire between the resistor and capacitor basically negating the resistor.

A simple software based low pass filter will most likely work as well but a little bit of hardware filtering is "the right way" and will provide some protection for the input.

/Henrik.