Ok! Thanx a lot, Joojaa! I`m waiting.....
BTW, I try expressions (like this)
float $len;
float $prev[];
float $le[];
$prev=joint -q -a -p joint3;
$le=joint -q -a -p joint4;
//print $le[1];
float $x;
float $y;
float $z;
$x=$le[0]-$prev[0];
$y=$le[1]-$prev[1];
$z=$le[2]-$prev[2];
$len=sqrt(($x*$x)+($y*$y)+($z*$z));
print $len;
joint4.Length=$len;
But I dont know how to lock in the $len to force Maya to calculate angels when I use a (let say) "translate to A" for a joint.