You raise a pretty good point about Asimov's Laws.
(My opinion of course)
Ash was prepared to allow the entire crew to die to protect the Alien (either by the Alien killing them, or Ash killing them himself). So the first Law is out the window.
I would imagine that because the Company sent in Ash to protect the Alien at all costs, that either Ash was not programmed with Asimov's Laws, or the Company disabled the First Law. You can't have your "inside man" disobeying its orders because of a Law to protect humans.
You could say that Asimov's Laws are meant to synthetically give a machine "morals". I wouldn't say that Ash's "crazy" behaviour was because he was conflicted as it would mean that he didn't "want" to kill Ripley.
For me Ash is the true antagonist in the film; the truly "evil" character. The Alien kills simply because of instinct and self preservation. While incredibly dangerous, it is neutral on the "Good and Evil" scale. Ash on the other hand is willing to do deplorable things.
(Of course this is how he was programmed, he has no free will either.

)
If nothing else, for me Ash is the "
face of the faceless Company", who put profit above lives. It is completely fitting that Ash "smirks" when he tells them "you're all dead."
Kevin