As a Big 'C' Catholic I'd have to disagree with Caleb's post on principle. But no holy wars or anything, I promise.
Catholics, like some Protestant congregations, truly consider themselves the Universal Church. Unlike other Protestant congregations however, we do not consider non-Catholics (or not-us'es) to not be Christians.
But, when Catholics say catholic in the Creed, we mean everybody capable of salvation, not just Christians.
"All men are called to this catholic unity of the People of God.... and to it, in different ways, belong or are ordered: the Catholic faithful, others who believe in Christ, and finally all mankind, called by God's grace to salvation."
As far as I know, Little 'c' catholic is a lot broader as defined by the Catholic Church than as it is defined by Protestants. I'm not sure how or why this teaching came about, but the Apostles Creed is old and the traditions passed on by it are old.
There's actually a pretty good tradition of adopting a thing common to most Christians to describe one group.
- Episcopal (a church with churches)
- Presbyterian (a church with leaders)
- Methodist (a church that follows a rule)
- Baptist (a church that practices baptism)
- Congregational (a church that has congregations)
- Church of Christ (a church with Christ as its founder)
- Evangelical (a church that proclaims the Gospel)
- Pentecostal (a church that started as a church at Pentecost)
- Orthodox (a church with right teaching)
Catholics would say we're all those things too.