"Not now Kato I'm busy"
Sorry crap Pink Panther gag.
Your first problem is that you can't break out individual parts from a mix - like if you want a vocal but not the backing you can't do it. Get used to it, that's just the way recorded music works (not totally, as you can mess around with eq/filters to get rid of some stuff, but it's not totally satisfactory). On the other hand, if you find a cool break that works as it is, then this is cool. For instance 'Loser' by Beck or 'Lately' by Massive Attack, or 'My Name Is' by Eminem or 'Lady' by Modjo, all built on breaks from other peoples tunes.
I don't know what sampler you've got, but loads of them have a 'timestretch/compression' feature on. This means that you can change the length of a sample without altering its pitch. It ain't perfect, but it's used all over the place.
I use
an E-mu E5000 Ultra which I use for sampling loops, but also for playing actual instrument sounds. It's great, I lurrve it.
If you have a small phrase sampler I guess you need to get into looping breaks in order to make music. I remember when I were a nipper taking a Stevie Wonder break, looping it (actually retriggering it) and putting some sampled vox over the top. I liked it.
Hope this helps,
KasioRoks