Hi Colin,

This is a common question; it's even in our searchable knowledge base.
There are a lot of quick answers there, so give it a try.

Jeffery Mirus writes very good articles; try this one:

Papal Infallibility by Jeffrey Mirus, PhD

Below is a link to the Council document that defined Papal Infallibility. It's important to remember that no one is inventing any new teaching here. Before 1869, all Catholics believed in Papal Infallibility. There just wasn't a need for a formal declaration to clarify misunderstandings among the faithful at the time. The same is true with teachings like Transubstantiation — before it was formally defined, every Catholic believed in the teaching. Our Church gets slandered often by others who say, "Catholics invented these teachings." No! The Church safeguards, protects and clarifies Our Lord's teachings for the faithful.

First Vatican Council (1869-1870) [EWTN] [Papal Encyclicals Online]

This one is long (a 2-pager) but will address your question:

• Can a Catholic receive Holy Communion if they don't believe all that the Church proposes? (Part 1)
  

I did a couple searches for you and found these set of postings that should also help:

• Search Result 1
• Search Result 2

Mike