Erik this is what I have done.
By the way I am driving an inductive load and I think it could be a cause to noise problem. How should I shield these wires coming out of this inductive load? What kind of shield?

Have Done:
-Get rid of each and every ground loop.
-Use a good power supply.
-Put the thing in a steel box (make sure you use one big enough to take care of the heat).

Have NOT Done:

-Use a supervisor chip, not the RC reset. What is it?.
-Put 100nf capacitors directly across all chips...
what all chips?
-Put a 4.7 or 10 uF tantalum directly across the '51.
accross what? Vcc and GND of micro? I have a filter now...
-Use a 4 layer board with ground and Vcc planes.
-Use differential serial communications (422/485).
-Put an VDR at raw power input. (What is this?)
-Opto-isolate all non-differential signals.
-Put ferrite beads on all wires at the place where they enter the box.
-Do not drive capacitive loads (like ribbon cables) from CMOS outputs...Do not have this in my design.


Thanks for your help Erik