hello EightBall,
FitCD and MovieStacker are only calculators to assist in producing your Avisynth script (.avs file). It's likely that your source will need to be resized to a resolution of one of the KVCD templates. If the source is dvd (ntsc) then the resolution is 720x480 and to encode that to kvcdx3 (528x480) you need a line like this is in the script:
BicubicResize(352, 350, 1/3, 1/3, 0, 1, 720, 47
FitCD and MovieStacker helps to fill in the right numbers. Also you can add various filters with these applications and they fill in the parameters for you- for example:
STMedianFilter(8, 32, 0, 0, 8, 32)
You could type in the numbers in parenthesis manually but MovieStacker will make it much easier because there are sliders to each parameter's description.
If you're not familiar with AviSynth then this probably won't make any sense but I hope this helps
ren