A song title can't really be copyrighted..
if a melody or chorus is attached strongly to that title, then you probably have a case for getting the copy taken out of circulation (or taking their profits).
A sample needs to be cleared before you sell it. It's pretty simple.
If you've not cleared it, you're effectively going to give the owners a right to take all the money you ever hope to make from it - as they still own it.
[google - bittersweet symphony copyright infringement ]
If you don't make any money from it, it's still not legal - but the worst that could probably happen is that they (owners) tell you to remove it from everywhere it's up.
If you sample a smaller act, or dj, or indy film - I find usually writing to them and accrediting them appropriately does the trick WITHOUT doing royalties. It's free advertising.
For anyone people might have heard, you have to go through the PRS/MCPS (UK) and contact the publishers / record labels.
For copyrighting riffs and such, that's more difficult. It's all down to the court on the day, and how much evidence, who released it first, who's got more money and ultimately luck.
A cover is much the same, you just pay royalties for the performance and the composition. Which you are all doing, even live, right?
