Usually when a takeover is announced, the stock of the company being acquired goes up and the stock of the acquirer goes down a few percent, but my expectation in this case is that it won't have a whole lot of impact in the short term. They've made this offer before (and Temple-Inland management rejected it) so it's probably not a surprise to anyone. It's an all cash offer, so no new shares will be issued as a result of it.
Long-term, if the integration of the two companies goes smoothly and IP management can run the TIN business more profitably (either due to synergies or more effective management), then it should be a benefit to IP's profits and the stock price. Many mergers don't go smoothly though, so there's definitely a risk that the merger will hold down IP profits and share price for awhile after the merger.