Several years ago, a company I was working for , located in Boston,
MA., went though a change of ownership : all the common stock of the company
was sold to a larger company. At the time, all the non-competes
included in the employement contracts and agreements had to be 
re-signed with the new company, because they were no longer
enforceable as a result of the ownership change.
I am currently working for a TX company, and I would like to know if a
change of ownership in my current company would void :
1- an existing employement agreement
2- a non compete that would be part of said agreement
3- and if not, was it a state law applicable only in MA?

I'm fearful your best interest often get lost in buy outs and mergers.
Appealling to the law occassionly is sucessful short term, but likely
will hurt you long term. It seems improbable that any one will enforce
the non compete agreement unless you devulge important corporate
secrets, but you could be fired from a subsequent job if you claim
there is no agreement. It is probable MA has some special laws, but a
good chance they little effect the real world in MA or elsewhere.
Lawyer boo hiss.  Neil