A couple different points:
1.) What I share in this post is from a practical Catholic's perspective. I am ok-versed (not necessarily well-versed by I do know a good deal of the official Catholic teachings) in the Catechism of the Holy Catholic Church, and I am not saying that you have to believe what I believe (despite the fact that I would hope that everyone were Catholic--I come with no false image). I am only presenting this information from the perspective of the teachings of the Church.
2.) The Book of Wisdom is found in the Catholic Bible. In most versions of the Bible (King James, New King James, etc.), the Books of Tobias, Judith, Wisdom, Ecclesiasticus, Baruch, 1 Machabees, and 2 Machabees from the Old Testament are omitted (I'm not quite sure why). The Deutero-Canonical Books are only found in Catholic Bibles.
3.) The Catechism of the Catholic Church's definition of the Trinity is: "The mystery of one God, in three Persons: Father, Son, and Holy Spirit. The revealed truth of the Holy Trinity is at the very root of the Church's living faith as expressed in the Creed. The mystery of the Trinity in itself is inaccessible to the human mind and is the object of faith only because it was revealed by Jesus Christ, the divine Son of the eternal Father." Therefore, we are monotheists, that is comprised of the Father, Jesus, and the Holy Spirit. Our God is a triune God, and the Father is God, Jesus is God, and the Holy Spirit, too, is God. You can imagine this concept as a triangle. You can look at any one corner of the triangle, but it's still the same. It may literally a different corner, but it's still the same angle measure and has the same properties as the other angles. In addition, to give a pretty good image, we say in the Nicene Creed "We believe in the Holy Spirit, the Lord, the giver of life, who proceeds from the Father and the Son. With the Father and the Son, He is worshipped and glorified." It's an idea of the Father, the Son and the Holy Spirit all with the same beginning as God, but as three different Persons.
4.) As for Mary: no, we do not worship her, and we do not believe that she is a god or comes anywhere near God's glory. Yes, she was chosen by God to be the mother of Jesus, but that does not at all make her non-human. We do venerate her, and call her Blessed. She was assumed (meaning she did not die) into Heaven because she had not sinned, and God made it possible for her to be born without Original Sin so that she may give birth to Jesus. We may also call her the Holy Mother (don't let that make you think that equate her with the same status as our Holy Father).
5.) A similar case for the Saints. In the Apostle's Creed, (which begins "I believe" not "We believe" like the Nicene Creed), it says, "I believe in...the communion of saints...". The idea that there is a communion of saints alludes to the fact that we are in a brotherhood with them. They are mortals who have died, but lived very holy lives and contributed great things to the world. It is true that there is a process for the canonization of a to-be Saint, and that process does mean that they have to have performed 2 miracles since their death. [Going into my own understanding of the canonization process, and I'm not sure how the Catholic Church understands the wording of it.] Rather, it's not that they are actually performing the miracle, but that they are causing it. Because the Catholic absolutely DOES NOT <b>worship</b> any Saint, it cannot be that while we are in prayer that we are praying to a particular saint as if we were praying to God. We ask the saint to pray for our sake to God! For example, in the Confiteor it says "I confess to Almighty God, and to you my brothers and sisters, that I have sinned through my own fault. In my thoughts and in my words, in what I have done, and in what I have failed to do. And I ask Blessed Mary ever virgin, to pray for me to the Lord, our God."
[back to official Catholic Doctrine.]
I do know, that when we pray to a saint, we pray to them as we might pray to a deceased member of the family. That person has specific meaning to us, and they have a specific connection to the family. When praying, we may ask them to look out for a younger child like a guardian angel. The angels are not God, but they do help us to form our prayers better, to hone them and focus in a certain way, and to model our lives better. Yes, our ultimate role model is Jesus, but sometimes a saint can offer wonderful inspiration and perhaps hase gone through similar trials in his/her life that we are going through at the present. But we, humans on earth and saints in heaven, belong to the same community as children of God. You wouldn't say that going to a good friend for help is raising them to God status, and you wouldn't say that asking your sister for help w/ talking to the girl you're sweet on were worshipping her. Ask any Catholic, and they will tell you that the saints were extremely holy people, and continue to intercede in our lives, but they--as all else does--fall short of the Glory of God.
6.) I just read in a couple of the posts the word "Eloi." I thought I'd make a quick note about when Jesus is on the cross, and he says "Eloi, Eloi, lama sabachthani." This is the beginning of Psalm 22, which has a general message of "I feel forsaken by all around me, and I cannot find you, yet how Holy art Thou." At the end of the Psalm, it says that all will turn to God and worship Him. I just thought I'd clear up a common misconception that Jesus was crying out and felt cast away--no, instead, He was telling all to look to the Lord for salvation, and that He will deliver unto us what He has promised. I don't know why I felt like I needed to share this, but I felt it is misconception enough that it deserved to be put here--although slightly irrelevant to the idea of Christianity as monotheistic.
Oh crud, I have to run. I'll give a follow-up post to some other things I was going to mention. Sorry for the digression at the end, and I hope this post was informative about the way Catholics believe, and what exactly we do believe.
). It's much more interesting to get the info from an 'insider' 
