The sample at the beginning of the Eminem's Without Me, is not, in fact, an "old school rap sample." Its the start of a song by Obie Trice, mystery rapper extroardinaire. The point of this track is to give the impression that Obie is being cut off for a new Eminem song (i.e. as if on the radio or TV, hence Eminem Show.)
Those familiar with Detroit rap or just the D12/Eminem mythos know of Mr. Trice as the underground rapper that can't seem to get respect in the mainstream world. For further study, might I recommend obietrice.org or Devil's Night LP track 15.