erk. We do not worship the Virgin Mary or the Saints. We venerate them and revere their example, yes. We do pray to them, but for their intercession, and not their intervention. The idea is the same as asking other people to pray for you. However, such prayer (while benefcial) is not required: the centre of the Catholic faith is and has always been Jesus Christ and the sacrifice he made for us at Calvalry.
There are actually a lot of theological differences between Catholics and Protestants, so I'll try to cover some of the major ones. I'm an engineer and not a theologian, so my explanations will necessarily be lacking. I'll also try to put together a list of resources to consult on this matter if you wish. Please keep in mind that I am not trying to start a theological debate on these matters, but to provide a short summary of key points. There are also many good people at
http://www.christianforums.com who can provide much better explanations.
1. Authority- Catholics and Orthodox christians do not hold that the bible is the sole source of authority in matters of faith. There is also Sacred Tradition. This entails both biblical interpretation as well some doctrines not found explicitly in the bible or only mentioned obliquely (such as Purgatory). These doctrines are all of ancient origin. Also Catholics believe that authority also rests in the living Magisterium of the Church which is the teaching authority of the popes, cardinals, bishops and so forth. Related to this is the matter of Petrine primacy, infallibility, apostolic succession an such like.
2. Soteriology- This concerns the matter of salvation. Protestants generally hold that salvation is through faith alone. We on the other hand, maintain a view that could best be described as "faith+works". In other words it is insufficient to simply believe in Christ without also acting on that faith.
3. Sacramentalism- In Catholicism and Orthodoxy, we hold that there are seven sacrements through which the Holy Spirit imparts grace to believers. The most important of these is the sacrament of communion: the holy Eucharist, in which the bread and the wine are the actual, physical body and blood of Christ.
4. Ecclesiology- We hold that the Catholic Church is the sole possesor of the fullness of the truth of Christian faith. It is the church instituted by Christ ("On this rock..", etc). This also relates directly to Petrine authority and apostolic succession.
There are many other specific doctrines, but this covers the most important ones. It can also be said that we view the world very differently than do (most) Protestants, owing to our differing theologies.