Ah... and KCC uses Qt5 now.
Well, I would in general advise one to ditch WinXP if possible. If you cannot afford new hardware, you can always install linux. I did, my laptop had XP and would never support Vista/7/8 -- but it runs most any linux just fine, and quite smoothly too. Unless the hardware is REALLY old, the processor probably supports sse2.
Failing that, you can build KCC yourself, via the tagged release, just install Qt, python, a few pypi modules, etc... shouldn't be too hard.
Or hope someone has a saved copy of the old installer. Your choice.