UBW Firmware modification problem

Hi guys, I downloaded the zipped files (D143.zip) from THE UBW page:
Index of /UBW/FW/D_143

And I wanted to modify the firmware program for my DIY XBee. The problem is the workspace file can't be opened!
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So I thought are the zipped files damaged, or do I need to upgrade my MPLAB 7.40?

Certainly 7.4 is VERY old now, I expect the UBW software uses a much later version.

okay, I just downloaded 8.46 now...

So I'm using MPLAB 8.46 now, which part of the files do I actually adjust in the myriad of source files? (and it's in C... argh.. I thought it is in assembly). I'll just be using the Rx-Tx pins using Manchester code to receive data wirelessly via RF modules.

Pardon me, but my programming experience goes up to only blinking LEDs and ADC, and some bit-testing. It's my achilles' heel I'd like to remedy.

**broken link removed**