Just cut the lead off the old PSU and patch it in to a molex connector. Hubs either work off 5V or 12V, so just check which you need. Red is usually 5V and yellow is 12V on a molex cable. I usually use those freebie molex->fan cables that come with cheap CPU and case fans.
how do i tell which cable to wire up? i know the center of the plug is positive but the cable has 2 black wires :S (i have some black replacement molex and pins that i can use...