In a recent opinion, the Texas bar's ethics committee found that a law firm must stop representing a litigation client if it hires a lawyer who formerly worked on the case as a law clerk at the firm representing the opposing party. Screening the tainted lawyer to prevent the sharing of any confidential information he learned in his prior employment won't enable the firm to continue representing the client. You can read the opinion here. Bloomberg/BNA has more on the story here.
Under the Model Rules, a firm would be allowed to continue the representation of the current client if it screened the newly hired attorney, but the rules in Texas are more strict when it comes to former client conflicts.