One may answer "Amen" to a Beracha that he hears while reciting Pesukeh De'zimra in the morning. Thus, for example, if one finished reciting Baruch She'amar – the introductory blessing to Pesukeh De'zimra – and then hears the Hazzan conclude Baruch She'amar ("Baruch Ata Hashem Melech Mehulal Be'tishbahot"), he answers "Amen." For that matter, if one hears the person next to him conclude Baruch She'amar after he had finished the blessing, then he answers "Amen." This applies to any Beracha, such as if a person hears someone who had arrived late reciting the Beracha over the Tallit of Tefillin. However, a number of Poskim (including the Ben Ish Hai and Hesed La'alafim) maintain that one may not answer "Amen" to a Beracha after he concluded Baruch She'amar unless he had proceeded to Mizmor Le'toda, the first chapter recited after Baruch She'amar. After all, Baruch She'amar is, as mentioned, the introductory blessing to Pesukeh De'zimra. Seemingly, then, just as one may not make any interruption after reciting a blessing over food before eating some of the food, one must likewise proceed immediately to Pesukeh De'zimra after reciting Baruch She'amar, without any interruption. Hacham Ovadia Yosef disagrees with this position, and maintains that one may answer "Amen" to a Beracha he hears after Baruch She'amar even before he began reciting Mizmor Le'toda. He concedes, however, that one should certainly try not to pause between the end of Baruch She'amar and Mizmor Le'toda so that no such interruption will be necessary. If one recites Baruch She'amar together with the Hazzan, and he concludes the blessing with the Hazzan, then he does answer "Amen" to the Hazzan's blessing, as this would give the appearance of answering "Amen" to his own Beracha, which is not permitted. This is true generally, as well – whenever one hears somebody finish a Beracha just as he finishes a Beracha, he does not answer "Amen," so as not to give the impression that he answers "Amen" to his own blessing. It is worth emphasizing in this context that Halacha forbids speaking after the recitation of Baruch She'amar, through the end of the Amida. Actually, as speaking is forbidden between the Amida and "Ana" and "Le'David," one may not talk at all until the end of those prayers. For matters involving a Misva, one may speak after Yishtabah, before beginning the Beracha of "Yoser Or." But general conversation is strictly forbidden from Baruch She'amar until after "Ana" and "Le'David." Certainly, this is a difficult Halacha for many to observe. We are a social community, and socializing and friendly conversation is undoubtedly something that we strongly encourage. In fact, for many, seeing friends is a motivation to come to the synagogue, and there is nothing wrong with that. Nevertheless, our primary reason for coming must be to pray properly, to spend time focusing on our relationship with Hashem through Tefilla. We must therefore delay our conversations until after the prayer service, and give the Tefilla and attention and respect that it deserves and that Halacha requires. Summary: One may not speak from Baruch She'amar through the end of "Ana Le'David" after the Amida. If one hears a Beracha while he recites Pesukeh De'zimra, he may answer "Amen." If one recites Baruch She'amar with the Hazzan, and ends the blessing at the same time as the Hazzan, then he does not answer "Amen." If, however, he completed Baruch She'amar before the Hazzan, then he answers "Amen." This applies even if he had yet to begin Mizmor Le'toda, but preferably one should recite Mizmor Le'toda immediately after completing Baruch She'amar, without any pause.