in short, if you ever have hopes of doing anything with the songs (aside from just playing them for your friends or family) and hope to ever make any money from them at all, then yes you need to get permission.
The Verve paid the price for sampling a Rolling Stones strings riff for their hit "Bitter Sweet Symphony."
Furthermore, I believe you'll not only have to get the publishing rights but the mechanical rights as well, because you'll be using a portion of the song (publishing) and the recording (mechanical). So ... like I said, if it's for anything more than friends and family, don't do it.
