In that case try using the samples that come with Reason. They are quite good. You can tweak anything to sound the way you want. Raw samples almost always sound weak, but they are meant to be played around with.

There is a good article in the May and June edition of Future Music. It's called Bionic Beats. Check it out if you get a chance. And it also comes with a DVD full of samples, so it's win-win for you.