We say the prayer Baruch She-amar ("Blessed is the One Who said") prior to Pesukei Dezimra ("the Psalms of Praise") and we say Yishtabach ("May he be Praised") after these.
One must be cautious to refrain from talking from the moment he begins Baruch She'amar until after he concludes the Eighteen Benedictions (The Amidah). Rem"a: And even if it is for the sake of performing a mitzvah one may not talk between Baruch Sheamar and Yishtabach [Beit Yosef quoting the Kol Bo][see below 53 and 54].
In between these psalms one may ask [of another's welfare] out of respect [for that person] and may reply greetings to any person. And in the middle of [one of] the psalms he may ask [of another's welfare] out of fear and he may reply out of respect.