So it's been pointed out that the MCE remote will only work with Media Portal and not the video player we use on the PC. The alternative is to use a general WinLIRC receiver and one of the magic profiles for the Harmony 880.
Which brings me to the rest of the mouse.
Here is a sample circuit for a WinLIRC receiver. It contains the following - 4.7μF electrolitic capacitor, 5V 100mA TO-92 78L05 voltage regulator, 4.7kOhm resistor, 1N4148 universal diode and a TSOP 1738 IR receiver. With the exception of the TSOP 1738 IR receiver, 4.7μF electrolitic capacitor (it only has a 0.47μF one :P) and the 78L05 regulator, the mouse's circuitboard contains all of these items.
I've pulled a 78L05 out of a dead motherboard (thank you bios update..), which means all I need now is an IR receiver, a .47µF cap, and hey presto, WinLIRC :D
Update: I work at a University.. I have a friend in the Electrical Engineering Department who I know fixes VCRs. I got the missing parts, I just had to take apart a VCR to get them. Meh! :D However, the IR sensor is two wire as well. It's on a sub assembly with a bunch of caps, a resistor and an IC which connects to the main board via three wires, but I don't know if it logically works as a transistor with a pre-amp like the specified component does, it may do, given the age of the thing. I also grabbed IR sensors out of two mice.. one has two wires, one had 4 (1 x NO, 1 x NC?), and I don't know how to adapt the circuit for them. Realistically, just buying the component for $5 would be easier, but where's the fun in that? :)