yeah, that's way the industry goes after people for sharing files and suing the crap out of them... in general the music lawyers want to go after the money but if you just happen to be unlucky enough to be targeted so they can make an example out of you, it will likely be costly in terms of money and possibly jail time...
two solutions really: make you own samples using your own music and effort, or just contact the people and ask - explain what you're doing and chances are you'll only end up having to pay royalities if you start making sales and airplay (at which point it won't be an issue...)
let's face it, if someone used samples from your efforts without paying you, you might not appeciate it...