[jack3dm]

Теперь работает всё замечательно. Так как я это и задумывал. Спасибо!
++d && --i
вместо
d++ && i--

var d = 0; i = 10;
for(; d < 10 || i > 0; ++d && --i, 
	document.write("d is = ", d, " i is = ", i, "<br />")){
	
		if(d ==6 || i == 3)
			break;
};

/*
d is = 1 i is = 9
d is = 2 i is = 8
d is = 3 i is = 7
d is = 4 i is = 6
d is = 5 i is = 5
d is = 6 i is = 4
*/