Tibetans often use the word "puja" not only for "offering rituals," which is the literal meaning, but for any sort of deity yoga meditation session. Such sessions usually do include "offerings," but also mantra recitation, praises, liturgical desciptions, and likely a period of silent or "formless" meditation.
Since it's a Kagyu center, the Chenrezig Puja is likely an expanded version of Tangtong Gyalpo's Chenrezig (Avalokiteshvara) practice, which usually includes: lineage prayer, refuge and generating bodhicitta, visualization, seven limb prayer, praises, prayer for the six realms, mantra recitation, silent meditation period, dissolution and reappearance, and a variety of long life and aspiration/dedication prayers. It's about an hour.
Here's a short version of the above: http://www.kdk.org/images/chenrezig_sadhana.pdf
This is the basic practice, most places will expand this with some additional prayers.
Tara Puja is likely Chogyur Lingpa's "essence of the two accumulations," from Zabtik Drolma Terma, which is the four mandala offering to Tara, with recitation of the Praises to the 21 Taras. It's longer--maybe 90 minutes?, and it's a somewhat more elaborate ceremonial ritual, with music (drums, cymbals, bells, etc.) and a lot of chanting. The link Tanaduk offered, above, contains most of the liturgy for this practice.
Hope that helps!