Most PICs have a few Schmitt Trigger inputs. Some have comparators. So
you can probably make it work without any additional hardware. Just use a
pin with a Schmitt Trigger input buffer, or the built-in comparator.

In the PIC data sheet, the port block diagrams show which pins have Schmitt
Trigger input buffers.

The Electrcal Specifications section of the data sheet shows what the min
and max input levels are for high/low signals on different input types.

As Keith mentioned, the simplest way would be to just use an IR module with
a built-in band-pass filter of 38 or 40kHz, and modulate your IR LED at the
band-pass frequency of the module.

These respond pretty fast with a low-going signal when the IR LED is on, and
high-going signal when it's off. They work pretty much the same on TTL or
Schmitt Trigger inputs.

They are also less sensitive to ambient light than most IR photo transistors,
and have built-in filters to block light outside the IR wavelength.

So you save a ton of board space, use fewer parts, and save yourself a little
hysteria..;}