great question. there are bigger differences between the catholic church and the protestant church. any christian denomination other than catholic is protestant. there are differences between the protestant denominations (lutherans, methodists, baptists, etc) but these are usually minor differences.
the main differences between catholics and protestants are:
- the authority of the pope
- the position and role of mary and the "saints"
- the role of the sacraments (baptism, marriage, communion, etc)
- the role of church tradition
also, the catholic bible has a few extra books that the protestant bible does not have.
the differences between the protestant denominations usually break down along the liberal/conservative lines. for example, methodists tend to be more liberal than baptists.
hope this helps.