Basically this is similar to the Jamaican dub technique - DJ Screw would take beats or melodies from songs and cut and paste the parts he liked together using rough transitions like scratches and skipped beats ("chopping"), while slowing down the tempo to make the beat sound slightly "off" ("screwing").
He did this in order to reproduce the effects that being "screwed" on "lean" has on one's perception of music.
"Lean" is Houston slang for codeine syrup.
The Screwed Up Click is basically a group of musically inclined friends and hangers-on of DJ Screw, many of whom were and are involved in the "lean" trade.
DJ Screw himself died of a codeine overdose, though some claim that his codeine was spiked with "ice" or methamphetamine.
Fat Pat may have died in a "lean" deal gone sour and the circumstances of Big Hawk's death look a little suspicious as well.
The Screwed Up Click is one of the most integrated hiphop crews in the US, with their major star right now being Paul Wall, a white Houstonian.
More info than I needed...