I had the same problem with properly grouping parts to my needs.
The default parts grouping that comes with MLCad did not at all fit my desires.
Unfortunately, MLCad does not support !CATEGORY yet, but still is one of my main building tools.
So I had to workaround that problem by customizing the parts grouping just by parts title,
and this worked surprisingly well.
Except for some strange parts not falling into any of these groups,
all other parts this way could be grouped as I needed.
You can find my grouping here:
http://forums.ldraw.org/showthread.php?tid=6387,6387
The default parts grouping that comes with MLCad did not at all fit my desires.
Unfortunately, MLCad does not support !CATEGORY yet, but still is one of my main building tools.
So I had to workaround that problem by customizing the parts grouping just by parts title,
and this worked surprisingly well.
Except for some strange parts not falling into any of these groups,
all other parts this way could be grouped as I needed.
You can find my grouping here:
http://forums.ldraw.org/showthread.php?tid=6387,6387